Catalysts, activating agents, support media, and related methodologies useful for making catalyst systems especially when the catalyst is deposited onto the support media using physical vapor deposition

ABSTRACT

Use of physical vapor deposition methodologies to deposit nanoscale gold on activating support media makes the use of catalytically active gold dramatically easier and opens the door to significant improvements associated with developing, making, and using gold-based, catalytic systems. The present invention, therefore, relates to novel features, ingredients, and formulations of gold-based, heterogeneous catalyst systems generally comprising nanoscale gold deposited onto a nanoporous support.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/756,635, filed Apr. 8, 2010 now U.S. Pat. No. 7,989,384, which is adivisional of U.S. patent application Ser. No. 10/948,012, filed Sep.23, 2004 (now issued as U.S. Pat. No. 7,727,931), which claimed thebenefit of U.S. Provisional Patent Application Ser. No. 60/506,623,filed on Sep. 26, 2003, the disclosures of all of which are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to gold-based catalyst systems, andparticularly to gold-based catalyst systems in which nanoscale goldparticles are immobilized on nanoporous support media.

BACKGROUND OF THE INVENTION

It has been known that ultra-fine, nanoscale gold particles exhibitspecific physical and chemical properties different from those of theordinary coarse gold grains (“Ultra-fine Particles” published by AgnePublishing Center in 1986). In particular, such ultrafine gold iscatalytically active and can be used as a catalyst for oxidizing carbonmonoxide to form carbon dioxide. The use of catalytically active goldalso has been proposed to catalyze other oxidation reactions such as theoxidation of carbonaceous soot in diesel exhaust streams, oxidation ofunsaturated and saturated hydrocarbons, and the like.

Generally, ultra-fine particles of gold are very mobile and possesslarge surface energies and, therefore, tend to coagulate easily. Infact, it has been difficult to prevent such coagulation from occurring,making ultrafine gold hard to handle. Such mobility is undesirableinasmuch as the catalytic activity of gold tends to fall off as itsparticle size increases. This problem is relatively unique to gold andis much less of an issue with other noble metals such as Pt and Pd.Therefore, the development of the methods to deposit and immobilizeultra-fine gold particles on a carrier in a uniformly dispersed statehas been desired.

The primary methods known to date to deposit catalytically active goldon various supports recently have been summarized by Bond and Thompson(G. C. Bond and David T. Thompson, Gold Bulletin, 2000, 33(2) 41) asincluding (i) coprecipitation, in which the support and gold precursorsare brought out of solution, perhaps as hydroxides, by adding a basesuch as sodium carbonate; (ii) deposition-precipitation, in which thegold precursor is precipitated onto a suspension of the pre-formedsupport by raising the pH, and (iii) Iwasawa's method in which agold-phosphine complex (e.g., [Au(PPh₃)]NO₃) is made to react with afreshly precipitated support precursor. Other procedures such as the useof colloids, grafting and vapor deposition meet with varying degrees ofsuccess.

These methods, however, suffer from serious difficulties resulting in asituation as aptly described by Wolf and Schuth (Applied Catalysis A;General 226 (2002) 2): (hereinafter the Wolf et al. article). “Althoughrarely expressed in publications, it also is well known that thereproducibility of highly active gold catalysts is typically very low.”The reasons for this serious reproducibility problem with these methodsinclude: the difficulty in controlling gold particle size, the poisoningof the catalyst by ions such as Cl, the inability of these methods tocontrol nano-sized gold particle deposition, the loss of active gold inthe pores of the substrate, the necessity in some cases of thermaltreatments to activate the catalysts, inactivation of certain catalyticsites by thermal treatment, the lack of control of gold oxidation state,and the inhomogeneous nature of the hydrolysis of gold solutions by theaddition of a base.

DE 10030637 A1 describes using PVD techniques to deposit gold ontosupport media. However, the support media exemplified in workingexamples are merely ceramic titanates made as described under conditionsin which the media would lack nanoporosity. Thus, this documents failsto appreciate the importance of using nanoporous media to supportcatalytically active gold deposited using PVD techniques. WO 99/47726and WO 97/43042 provide lists of support media, catalytically activemetals, and/or methods for providing the catalytically active metalsonto the support media. However, these two documents also fail toappreciate the benefits of using nanoporous media as a support forcatalytically active gold deposited via PVD. Indeed, WO 99/47726 listsmany supports as preferred that lack nanoporosity.

In short, gold offers great potential as a catalyst, but thedifficulties involved with handling catalytically active gold haveseverely restricted the development of commercially feasible,gold-based, catalytic systems.

SUMMARY OF THE INVENTION

We have discovered that the use of physical vapor depositionmethodologies to deposit nanoscale gold on activating, nano-poroussupport media makes the use of catalytically active gold dramaticallyeasier and opens the door to significant improvements associated withdeveloping, making, and using gold-based, catalytic systems. The presentinvention, therefore, relates to novel features, ingredients, andformulations of gold-based, heterogeneous catalyst systems generallycomprising nanoscale gold deposited onto a nanoporous support. The manyaspects of the invention provide significant advances in areas includingbut not limited to catalyst deposition onto support media (especiallydeposition of catalytically active gold onto a nanoporous support),catalyst support structure, catalyst system design, catalyst activatingagents, and methods of using activating agents to enhance theperformance of catalytic systems. Some aspects of the present inventionalso generally are applicable to a wider range of other catalysts suchas platinum, palladium, rhodium, ruthenium, molybdenum, iridium, copper,silver, nickel, iron, and the like.

The gold-based catalyst systems of the present invention have excellentcatalytic performance. These systems would find application in the areaof CO abatement in the form of personal, vehicle and buildingprotection, catalysts and catalyst supports for the purification ofexhaust gases from internal combustion engines, removal of CO from fuelcell feedstocks, and in catalyzing other oxidation reactions such as theoxidation of carbonaceous soot in diesel exhaust streams and theselective oxidation of organic compounds. For instance, the gold-basedcatalyst systems would be suitable as catalyst systems for the catalyticoxidation of unsaturated and saturated hydrocarbons. The termhydrocarbon means unsaturated or saturated hydrocarbons such as olefinsor alkanes. The hydrocarbon can also contain heteroatoms like N, O, P, Sor halogens. The organic compounds to be oxidized may be acyclic,monocyclic, bicyclic, or polycyclic and may be mono-olefinic,di-olefinic, or poly-olefinic. The double bonds in compounds with two ormore double bonds may be conjugated or non-conjugated.

As an overview, one aspect of the invention involves using physicalvapor deposition (PVD) methodologies to deposit one or morecatalytically active metals such as gold onto a nanoporous support. Someembodiments of nanoporous supports have very high surface areathroughout the volume of the support, and conventional methodologiesinvolve impregnating such media as much as possible throughout theirvolume with catalyst. Indeed, the technical literature reports that such“full volume” impregnation may be required to achieve acceptablecatalytic performance. However, PVD tends to be a line of sight coatingtechnique, meaning that PVD deposits catalyst mainly at and very near(some minor surface penetration will occur, such as by diffusion) thesurface of the nanoporous support media. From a conventionalperspective, the nanoporous media appears to be underutilized, making itappear as if PVD were an inappropriate technique to be used in thiscontext. However, we have found that surface deposition/coating ofcatalytically active metal onto the nanoscale topography of nanoporousmedia provides catalyst systems with excellent performancenotwithstanding conventional wisdom. In the case of gold, for example,it appears that these nanoscale features help to immobilize the gold,preventing gold accumulation that might otherwise result in a loss ofperformance. In short, the present invention appreciates that nanoporoussupport media have more to offer catalytically than just high surfacearea throughout the volume of the media.

Some aspects of the invention carry out PVD of catalytically activemetal in unique ways. In one approach, support media is both tumbled (orotherwise fluidized) and comminuted (e.g., ground or milled) to somedegree during at least a portion of the PVD treatment. It has been foundthat comminuting the media during PVD enhances performance of theresultant catalyst system.

In other aspects, PVD is used to deposit a catalytically active metalsuch as gold separately from and after the support media has beenimpregnated with an activating agent. In short, preferred modes ofpractice involve depositing gold via PVD only after the support mediahas been impregnated with one or more activating agents, dried, andoptionally calcined. This greatly expands the range of activating agentsthat can be used in combination with a catalytically active metal. Wecan use ingredients that would otherwise react or be too soluble insolution when wet methods are used to deposit gold. For instance, theprocess of the invention can deposit gold or other metals onto mediacomprising very basic or water soluble materials. This has opened thedoor to testing and using water soluble, metal salts as activatingagents inasmuch as these are not washed away when gold is subsequentlydeposited via PVD. It would not be very practical to attempt to use suchsalts as activating agents when gold is impregnated onto the supportmedia via solution processing, inasmuch as the gold solutions could washaway the water soluble material and/or be chemically incompatible withthe activating agents (e.g., gold solutions tend to be strongly acidic,e.g., HAuCl₄).

Water soluble salts such as alkali metal salts and/or alkaline earthmetal salts are inexpensive, readily available, and easily incorporatedinto catalytic systems when practicing the present invention.Significantly, it has been discovered that these salts are potentactivators for gold-based catalysis, especially when used to activatenanoporous carbon support media. Bifurcating PVD deposition ofcatalytically active gold from earlier activation of the support mediawas a key to help enable this advance in the use of carbon mediasupports with activating salts for gold-based catalysis.

The present invention offers many other features and advantages. First,we have observed that a catalytically active metal such as gold isactive right away when deposited via PVD. There is no need to heat treatthe system after gold deposition as is the case with some othermethodologies. We anticipate that other precious metals may also notrequire a heating step after deposition. This, of course, does not meanthat a heating step, if desired, is not possible. It is within the scopeof the present invention to include a subsequent heating step.Additionally, the gold is highly active catalytically for relativelylong periods with respect to CO oxidation, even though it tends to bedeposited only proximal to the support media surface when using PVD todeposit the gold. The catalyst systems also are effective in humidenvironments and work over a wide temperature range, including roomtemperature (e.g., about 22° C. to about 27° C.) and much cooler (e.g.,less than 5° C.).

The physical vapor deposition process is very clean in the sense thatthere are no impurities introduced into the system as in the case of thesolution state processes. In particular, the process may bechloride-free and thus there is no need for washing steps to removechloride or other undesirable ions, molecules or reaction by-products,as is the case in most solution state deposition processes.

By using this process, very low levels of metal are required for highactivity. While most research in this area uses at least 1% by weightgold to achieve activity, and often times much more than 1 weight % goldto achieve high activity, in this work we have achieved very highactivity at 0.05% by weight gold or lower. This reduction in the amountof precious metal required for high activity provides a very substantialcost savings.

The catalyst system is robust and consistent. For example, we preparedand tested two identical embodiments of our system about one monthapart. Notwithstanding the fact that the two embodiments were separatelymade, the respective data for each were identical for practicalpurposes. This kind of consistency is uncommon for gold-based catalystsystems. See the Wolf et al. article.

This process results in a very uniform product with respect to preciousmetal concentration per particle and metal nanoparticle size and sizedistribution. TEM studies have shown that our process can deposit goldin a form including discrete nanoparticles and small clusters or in amore continuous thin film depending on what is desired. In general, itis desired to include gold in nanoparticle/small gold cluster form.

This catalyst preparation method can deposit catalyst metals uniformlyon non-uniform or non-homogeneous surfaces. This is not true for thesolution state deposition processes wherein solution deposition favorsdeposition on the surfaces having a charge opposite to the depositingmetal ion, leaving the other surfaces uncoated or at best weakly coated.

The PVD process can be used to deposit other metals simultaneously orsequentially or to deposit mixtures of metals by using poly-phasictargets so that catalyst particles can be formed that comprisepolyphasic nanoparticles, e.g., nanoparticles comprising atomic mixturesof say M₁and M₂ (where M₁ and M₂ represent different metals), or thathave combinations of metal nanoparticles for multi-function catalysts,e.g., nanoparticle mixtures comprising mixtures of discrete M₁ particlesand discrete M₂ particles. In this fashion, catalyst particles can beprepared that can catalyze more than one reaction and these functionscan be carried out simultaneously in practice. Thus, a catalyst particlecan be prepared that will oxidize CO while at the same time oxidizeNO_(x) efficiently.

This process can efficiently deposit catalytically active metals on awider range of support media, e.g., fibers or scrims. While fibers canbe coated in the solution coating processes, the shear used to pulp anddisperse the fibers generally results in dust formation and ininefficient coating due to the abrasion of the fibers during the coatingprocess. The catalytic fibers can be used to produce novel, highlycatalytically active felts, fabrics and fiber scrims.

This new process allows the creation of a new family of active metals oncarbon and on other oxidatively sensitive substrates. In the processesknown in the art that require a heating step to affix and activate thecatalyst particles, carbon in the presence of an oxidizing environmentcannot withstand the elevated temperatures that are often required.Thus, the carbon particles had to be treated in a reducing atmospheresince they would be attacked by oxygen during this heating step. Such areducing step may undesirably reduce other catalyst constituents (e.g.,as in the case of iron oxide supported on carbon or in porous carbon).In the instant invention, carbon particles and other non-oxide particlescan be coated with catalyst nanoparticles and no heating step or postreduction is required. In this manner, high surface area carbon can berendered catalytic for CO oxidation without losing the adsorptiveproperties of the porous carbon for the removal of other impurities froma gas steam.

This new process can be used to coat very fine particles of catalystsupport so that the fine particles can then be coated onto a secondgranular phase or can be formed into a porous granule to provide high COoxidation activity while providing low back pressure during use.

A method of making a heterogeneous catalyst system is provided in oneaspect of the present invention. The method comprises a step ofphysically vapor depositing catalytically active gold onto a nanoporoussupport medium.

A heterogeneous catalyst system is provided in another aspect of thepresent invention. The system comprises a nanoporous support medium. Thenanoporous support medium includes at least one water soluble saltimpregnated onto the support medium. The nanoporous support medium alsoincludes catalytically active gold deposited onto the support medium,wherein the catalytically active gold is deposited at a PenetrationDepth Ratio in the range of from about 1×10⁻⁹ to about 0.1.

In another aspect of the present invention a heterogeneous catalystsystem is provided that comprises a nanoporous support medium, an alkalimetal salt impregnated onto the support medium, and catalytically activegold deposited onto the support medium.

A method of making a catalyst system is also provided in accordance withan aspect of the present invention. The method includes a step ofimpregnating a water soluble salt onto a catalyst support medium. Themethod also includes a step of heat treating the impregnated supportmedium at a temperature greater than about 200° C. Additionally, themethod includes a step of physically vapor depositing a catalyst ontothe heat treated support medium.

In another aspect of the present invention a method of making a catalystsystem is provided. The method comprises a step of physically vapordepositing a catalyst onto a catalyst support medium. The method alsoincludes a step of mixing and comminuting the support medium during atleast a portion of the physical vapor deposition.

Also, a heterogeneous catalyst system comprising catalytically activegold deposited onto an activated carbon support medium is provided inanother aspect of the present invention.

In yet another aspect of the present invention a method of making aheterogeneous catalyst system is provided. The method includes a step ofdetermining information indicative of the impact that a water solublesalt has upon the catalytic activity of gold that is physically vapordeposited onto a support medium impregnated with the salt. The methodalso includes a step of using the information to make a catalyst systemderived from ingredients comprising the salt, the medium, and gold.

Additionally, in another aspect of the present invention, a method ofmaking a catalyst system is provided. The method includes a step ofimpregnating a water soluble salt onto a catalyst support medium. Themethod also includes a step of physically vapor depositing catalyticallyactive gold onto the impregnated support medium.

In a further aspect, the present invention relates to a method ofactivating a substrate surface is provided. This method includes a stepof hydrolyzing a metal alkoxide onto a catalyst support medium. Themethod includes a step of depositing catalytically active metal onto theactivated support surface and includes gold as the active metal andphysical vapor deposition as the method of depositing said metal.

In yet a further aspect, the present invention relates to a method ofproducing an enhanced surface area particle for support of active metalcatalysts is disclosed. The method includes incorporating smaller,nanoporous particles (i.e., guest particles) onto a coarser particle(i.e., host particle). The method includes depositing a catalyticallyactive metal onto the enhanced surface area support and includes gold asthe active metal and physical vapor deposition as the method ofdepositing said metal. The ratio of the average particle size of thehost particles to the guest particles is desirably in the ratio of10,000:1 to 10:1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a TEM image of a cross-section of a representative catalystsurface of the present invention (material of example 3).

FIG. 2 is a schematic side view of an apparatus for carrying out a PVDprocess for depositing catalytically active gold onto a support.

FIG. 3 is a schematic perspective view of the apparatus of FIG. 2.

FIG. 4 shows testing system that was used to subject samples to COchallenges in order to assess catalytic characteristics for oxidizingCO.

FIG. 5 schematically shows a system used for chromatographic analysis ofcatalytic characteristics of samples.

FIG. 6 is a graph showing catalytic characteristics of a sample, whereinthe ability of the sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 7 is a graph showing catalytic characteristics of a sample, whereinthe ability of the sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 8 is a graph showing catalytic characteristics of a sample, whereinthe ability of the sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 9 is a graph showing catalytic characteristics of a sample, whereinthe ability of the sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 10 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 11 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 12 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 13 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 14 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 15 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 16 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 17 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 18 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 19 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 20 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 21 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 22 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 23 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 24 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 25 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 26 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 27 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 28 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 29 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 30 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 31 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 32 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 33 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 34 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 35 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 36 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 37 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 38 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 39 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 40 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 41 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 42 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 43 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 44 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 45 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 46 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 47 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 48 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 49 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 50 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 51 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 52 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 53 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

FIG. 54 is a graph showing catalytic characteristics of samples, whereinthe ability of each sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 55 is a graph showing catalytic characteristics of samples, whereinthe ability of each sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 56 is a graph showing catalytic characteristics of samples, whereinthe ability of each sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 57 is a graph showing catalytic characteristics of samples, whereinthe ability of each sample to catalytically oxidize CO to CO₂ in a flowcontaining CO in air is depicted as a function of time.

FIG. 58 is a graph showing catalytic characteristics of a sample,wherein the ability of the sample to catalytically oxidize CO to CO₂ ina flow containing CO in air is depicted as a function of time.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention. While the present invention will be described in the specificcontext of gold-based catalyst systems, the principles of the inventionare applicable to other catalyst systems as well.

In the practice of the present invention, catalytically active gold isdeposited onto the desired support(s) using physical vapor deposition.Physical vapor deposition refers to the physical transfer of gold from agold-containing source or target to the support. Physical vapordeposition may be viewed as involving atom-by-atom deposition althoughin actual practice, the gold may be transferred as extremely fine bodiesconstituting more than one atom per body. Once at the surface, the goldmay interact with the surface physically, chemically, ionically, and/orotherwise.

Physical vapor deposition typically occurs under temperature and vacuumconditions in which the gold is very mobile. Consequently, the gold isquite mobile and will tend to migrate on the surface of the substrateuntil immobilized in some fashion, e.g., by adhering to a site on orvery near the support surface. It is believed that sites of adhering caninclude defects such as surface vacancies, structural discontinuitiessuch as steps and dislocations, interfacial boundaries between phases orcrystals or other gold species such as small gold clusters. It is adistinct advantage of the invention that the deposited gold isimmobilized effectively in a manner in which the gold retains a highlevel of catalytic activity. This is contrasted to those conventionalmethodologies in which the gold accumulates into such large bodies thatcatalytic activity is unduly compromised or even lost.

There are different approaches for carrying out physical vapordeposition. Representative approaches include sputter deposition,evaporation, and cathodic arc deposition. Any of these or other PVDapproaches may be used, although the nature of the PVD technique usedcan impact catalytic activity. For instance, the energy of the physicalvapor deposition technique used can impact the mobility, and hencetendency to accumulate, of the deposited gold. Higher energy tends tocorrespond to an increased tendency of the gold to accumulate. Increasedaccumulation, in turn, tends to reduce catalytic activity. Generally,the energy of the depositing species is lowest for evaporation, higherfor sputter deposition (which may include some ion content in which asmall fraction of the impinging metal species are ionized), and highestfor cathodic arc (which may be several tens of percents of ion content).Accordingly, if a particular PVD technique yields deposited gold that ismore mobile than might be desired, it may be useful to use a PVDtechnique of lesser energy instead.

Physical vapor deposition generally is a line of sight/surface coatingtechnique between the gold source and the support. This means that onlythe exposed, outer surfaces of the support, but not the inner pores wellwithin the substrate, are directly coated. Inner surfaces not in adirect line of sight with the source will tend not to be directly coatedwith gold. However, we have found by TEM analysis that after depositionon the surface of a porous substrate, the gold atoms can migrate bydiffusion or other mechanism some moderate distance into the catalystsurface to provide nano-particles and gold clusters in the substratepores in the region immediately adjacent to the surface before beingimmobilized. The average penetration into the porous substrates can beup to 50 nanometers in depth or sometimes greater, such as up to about70 to about 90 nm in depth. In general though, the penetration depth isless than 50 nm and can be less than 30 nm. The gold penetration is veryshallow compared to the typical support size.

The total thickness of the gold, or C_(t), is equal to the goldpenetration depth plus the thickness of the gold that is deposited onthe surface of the substrate and that has not penetrated by diffusion.This total thickness is in general less than 50 nm and can often be lessthan 30 nm or even less than 20 nm. On materials having surface poreswhose depth is greater than about 10 nm to 20 nm, the total goldthickness can appear to be greater than 50 nm since the gold layerfollows the contours of the surface and the actual surface contour isreflected by the pore structure that it possesses. It is most preferredthat the active gold species be collected on the outermost portion ofthe catalyst particle since this is the surface of the catalyst thatinteracts most readily with gaseous reactants.

The thickness of the gold shell region relative to the catalyst supportparticle size is quantified by the formulaPDR=C _(t) /USTwherein PDR is the penetration depth ratio, UST is the underlyingsupport thickness or particle size and C_(t) is the total thickness ofthe gold, as defined above. The underlying support thickness representsthe size of the support as measured perpendicular to the catalystsurface and is usually indicative of particle size. The underlyingsupport thickness may be determined by microscopic methods includingoptical microscopy or scanning electron microscopy. The value for C_(t)may be determined by transmission electron microscopy in the case ofthin films and high resolution scanning electron microscopy in the caseof thicker films. The total thickness C_(t) is very easily discernedfrom visual inspection of TEM data. Because of the uniformity by whichgold is coated, a single representative TEM picture can be effective tocharacterize the coating. In practice, a sample may be effectivelycharacterized via examination of a number of TEM pictures of catalystsurface cross-sections (vida infra). In preferred embodiments, PDR is inthe range of from about 1×10⁻⁹ to 0.1, preferably 1×10⁻⁶ to 1×10⁻⁴,indicating that the gold shell region is very thin indeed relative tototal support thickness. As noted above, this generally corresponds to apenetration depth on the order of up to about 50 nm, preferably about 30nm on preferred supports.

Characterization of the surface region and the gold bodies isaccomplished using transmission electron microscopy as is well-known inthe catalyst art. One method suitable for characterizing the catalyticsurfaces is as follows: the catalyst particles are embedded in 3MScotchcast™ Electrical Resin #5 (epoxy; 3M Company, St. Paul, Minn.) indisposable embedding capsules; resin is allowed to cure at roomtemperature for 24 hours.

For each sample, a random, embedded granule is trimmed (with a stainlesssteel razor blade previously cleaned with isopropyl alcohol) down to themiddle surface region of the granule such that most of the granule iscut away on one side, leaving epoxy on the on the other side. A smalltrapezoid-shaped face (less than a half millimeter on a side) isselected and trimmed such that the epoxy/granule interface is leftintact. The long direction of this interface is also the cuttingdirection. A Leica Ultracut UCT microtome (Leica Microsystems Inc.,Bannockburn, Ill.) is used to cross-section the face. The face is firstaligned such that the granule surface was perpendicular to the knifeedge. Sections approximately 70 nm thick are cut at a speed of 0.08mm/second. These sections are separated by floating onto deionized waterand collected using a microtomy hair tool and picked up using a “PerfectLoop” (loop distributed by Electron Microscopy Sciences, FortWashington, Pa.). Samples are transferred via this loop to a 3 mmdiameter, 300 mesh copper TEM grid with carbon/formvar lacey substrate.The regions of interest (intact, cleanly cut specimens showing theinterfacial region) that lie over the holes in the substrate are imagedand analyzed.

Images are taken at various magnifications (50,000× and 100,000×) in aHitachi H-9000 transmission electron microscope (TEM; Hitachi HighTechnologies America, Pleasanton, Calif.) at 300 KV accelerating voltageusing a Gatan CCD camera (Gatan Inc., Warrenton, Pa.) and DigitalMicrograph software. Representative regions (regions selected whereinthe interface of the catalytic surface is clearly examined in a fashionperpendicular to the surface of the sample) are imaged. Calibratedmarkers and sample identifications are placed on each image. Numerous(>10) interfacial regions are examined.

An example of a TEM image of a cross-section of a representativecatalyst surface of the present invention (material of example 3) isshown in FIG. 1. The gold nanoparticles can be seen to be both on thesurface of the support and in the sub-surface region of the support. Theregion containing the gold nanoparticles is very thin and the golddeposition can be seen to follow the contours of the surface of thesupport.

As a consequence of line of sight coating, the resultant catalyticallyactive material of the invention from one perspective may be viewed asnanoporous catalytic supports having relatively thin shells ofdiscontinuous, catalytic gold on and proximal to their outer surfaces.That is, a resultant catalytically active material comprises a gold-richshell region proximal to the surface and an interior region comprisingnegligible gold. In preferred embodiments, this gold-rich shell regioncomprises small (generally less than 10 nm, most preferably less than 5nm), discrete gold bodies.

The inventive approach of forming a catalytically active shell regiononly on the surface of a nanoporous support is contrary to conventionalwisdom when developing new catalytic material, and, therefore, the factthat the resultant material is so catalytically active is quitesurprising. Specifically, the present invention puts catalyticfunctionality only near the surface of a highly porous support. Interiorporosity is purposely unused. From a conventional perspective, it seemspointless to underutilize a nanoporous support in this manner. Knowingthat catalytically active metal is to be deposited only at the supportsurface, the conventional bias might have been to use a nonporoussubstrate when depositing catalytically active gold onto a support. Thisis especially the case when PVD is not able to access the interior ofthe porous support in any event. The present invention overcomes thisbias through the combined appreciation that (1) gold mobility is highlyrestricted on the surface of nanoporous supports, and (2) gold is stillcatalytically active even at very low weight loadings resulting from thesurface coating approach. Consequently, using such supports is highlyand uniquely beneficial in the context of depositing gold onto thesurface region of a nanoporous support even though full catalyticcapacity of the support is not utilized.

Generally, physical vapor deposition preferably is performed while thesupport to be treated is being well-mixed (e.g., tumbled, fluidized, orthe like) to help ensure that particle surfaces are adequately treated.Methods of tumbling particles for deposition by PVD are summarized inU.S. Pat. No. 4,618,525. For methods specifically directed at catalystssee Wise: “High Dispersion Platinum Catalyst by RF Sputtering,” Journalof Catalysis, Vol. 83, pages 477-479 (1983) and Cairns et al U.S. Pat.No. 4,046,712. More preferably, the support is both tumbled or otherwisefluidized as well as comminuted (e.g., ground or milled to some degree)during at least a portion of the PVD process. This provides a degree ofmechanical abrasion of the surface of the particles and generation ofsome fines during gold deposition. Our data suggests that catalyticperformance is enhanced when deposition is carried out with comminution.It is our belief that these processes, i.e., the generation of fines andthe mechanical interaction of the grits with each other, increases theactivity of the resulting catalyst materials. While not wishing to bebound by theory, we believe that the fines provide higher surface areafor higher activity. Fresh surface areas of the support are alsoexposed, and this might also enhance performance.

The impact of such comminution upon the resultant surfacecharacteristics of the catalyst system were studied via TEM analysis. Inthe case of the gold on carbon containing the activating agents of thepresent invention, the TEMs reveal the presence of a unique, two phasestructure believed to comprise nanoparticles and clusters of gold andcarbonaceous material on the surface of the gold-coated particles. It ispossible that the mechanical action gives rise to this unique structureas carbonaceous material from one granule is transferred onto thegold-coated surface of another granule by rubbing. This nano-compositeof gold/activation agent and carbon seems to possess a very highactivity for catalysis of CO oxidation.

An apparatus 10 for carrying out the preferred PVD process is shown inFIGS. 2 and 3. The apparatus 10 includes a housing 12 defining a vacuumchamber 14 containing a particle agitator 16. The housing 12, which maybe made from an aluminum alloy if desired, is a vertically orientedhollow cylinder (45 cm high and 50 cm in diameter). The base 18 containsa port 20 for a high vacuum gate valve 22 followed by a six-inchdiffusion pump 24 as well as a support 26 for the particle agitator 16.The chamber 14 is capable of being evacuated to background pressures inthe range of 10⁻⁶ torr.

The top of the housing 12 includes a demountable, rubber L-gasket sealedplate 28 that is fitted with an external mount three-inch diameter dcmagnetron sputter deposition source 30 (a US Gun II, US, INC., San Jose,Calif.). Into the source 30 is fastened a gold sputter target 32 (7.6 cm(3.0 inch) diameter×0.48 cm ( 3/16 inch) thick). The sputter source 30is powered by an MDX-10 Magnetron Drive (Advanced Energy Industries,Inc, Fort Collins, Colo.) fitted with an arc suppressing Sparc-le 20(Advanced Energy Industries, Inc, Fort Collins, Colo.).

The particle agitator 16 is a hollow cylinder (12 cm long×9.5 cmdiameter horizontal) with a rectangular opening 34 (6.5 cm×7.5 cm) inthe top 36. The opening 34 is positioned 7 cm directly below the surface36 of the gold sputter target 32 so that sputtered gold atoms can enterthe agitator volume 38. The agitator 16 is fitted with a shaft 40aligned with its axis. The shaft 40 has a rectangular cross section (1cm×1 cm) to which are bolted four rectangular blades 42 which form anagitation mechanism or paddle wheel for the support particles beingtumbled. The blades 42 each contain two holes 44 (2 cm diameter) topromote communication between the particle volumes contained in each ofthe four quadrants formed by the blades 42 and agitator cylinder 16. Thedimensions of the blades 42 are selected to give side and end gapdistances of either 2.7 mm or 1.7 mm with the agitator walls 48.Preferred modes of use of this apparatus are described below in theexamples.

The gap spacing between the agitator 16 and the walls of the housing 12affects the performance of the resulting catalyst. As the gap is madesmaller, the support particles will have a greater tendency to be groundto some degree. Since such grinding is believed to be beneficial, thegap is set at a suitable distance to ensure that grinding occurs. In onepreferred mode the gap was set at about the diameter of the supportparticles to be coated.

Physical vapor deposition may be carried out at any desiredtemperature(s) over a very wide range. However, the deposited gold maybe more catalytically active if the gold is deposited at relatively lowtemperatures, e.g., at a temperature below about 150° C., preferablybelow about 50° C., more preferably at ambient temperature (e.g., about20° C. to about 27° C.) or less. Operating under ambient conditions ispreferred as being effective and economical since no heating or chillingrequirements are involved during the deposition

While not wishing to be bound by theory, it is believed that thedeposition at lower temperatures yields more catalytically active goldfor at least two reasons. First. lower temperatures yield gold with moredefects in terms of geometrical size and/or shape (angularities, kinks,steps, etc.). Such defects are believed to play a role in many catalyticprocesses (see Z. P. Liu and P. Hu, J. Am. Chem. Soc., 2003, 125, 1958).On the other hand, deposition at higher temperatures tends to yield goldthat has a more organized and defect-free crystal structure and hence isless active. Additionally, deposition temperature can also impact goldmobility. Gold tends to be more mobile at higher temperatures and hencemore likely to accumulate and lose catalytic activity.

The present invention provides catalytically active gold on the desiredsupport(s) to form heterogeneous catalytic systems of the presentinvention. Gold is widely known as a noble, relatively inert metal witha yellowish color. However, the characteristics of gold changedramatically in nanoscale regimes, where gold becomes highlycatalytically active. The high reactivity of gold catalyst in comparisonwith other metal catalysts is illustrated by reactions such as oxidationof CO under ambient conditions and reduction of NO, as well asepoxidation and hydrochlorination of unsaturated hydrocarbons.

In preferred embodiments, catalytically active gold may be identified byone or more requisite characteristics including size, color, and/orelectrical characteristics. Generally, if a gold sample has one or moreof these requisite characteristics, and preferably two or more of thesecharacteristics, it will be deemed to be catalytically active in thepractice of the present invention. Nanoscale size is a key requisiteassociated with catalytically active gold in that the catalytic activityof gold to a large degree is a function of whether the gold sample has athickness dimension in the nanoscale regime (e.g., particle diameter,fiber diameter, film thickness, or the like). Bodies (also referred toas clusters in the literature) having smaller dimensions tend to be morecatalytically active. As size increases, catalytic characteristics falloff rapidly. Accordingly, preferred embodiments of catalytically activegold may have a nanoscale size over a wide range, with smaller sizesmore preferred when higher activity is desired. As general guidelines,catalytically active gold has particle or cluster dimensions in therange of from about 0.5 nm to about 50 nm, preferably about 1 nm toabout 10 nm. Preferably, the gold has a size of no more than about 2 nmto about 5 nm in any dimension. The technical literature reports thatcatalytic activity may be a maximum at sizes in the range of from about2 nm to about 3 nm. The size of the individual gold nanoparticles can bedetermined by TEM analysis as is well known in the art and as isdescribed herein.

In terms of color, gold in larger scale size regimes has a yellowishcolor. However, in the nanoscale size regimes in which gold iscatalytically active, the color of gold becomes a reddish pink whenviewed under white light, although very small clusters of gold and goldsurface species can be colorless. Such colorless species can be quitecatalytic, and the presence of such colorless species is usuallyaccompanied by some colored nanoparticles of gold. Consequently,determining if the color of a gold sample includes a noticeable reddishpink component and/or is colorless indicates that it is possible thatthe sample is catalytically active.

The amount of catalytically active gold provided on a support can varyover a wide range. However, from a practical perspective, it is helpfulto consider and balance a number of factors when choosing a desiredweight loading. For instance, catalytically active gold is highly activewhen provided on nanoporous supports in accordance with the practice ofthe present invention. Thus, only very low weight loadings are needed toachieve good catalytic performance. This is fortunate, because gold isexpensive. For economic reasons, therefore, it would be desirable not touse more gold than is reasonably needed to achieve the desired degree ofcatalytic activity. Additionally, because nanoscale gold is highlymobile when deposited using PVD, catalytic activity may be compromisedif too much gold is used due to accumulation of the gold into largebodies. With such factors in mind, and as general guidelines, the weightloading of gold on the support preferably is in the range of 0.005 to 10weight %, preferably 0.005 to 2 weight %, and most preferably from 0.005to 1.5 weight % based upon the total weight of the support and the gold.

Depositing catalytically active gold onto a support is very compatiblewith PVD techniques. Gold naturally sputters to form catalyticallyactive, nanoscale particles and clusters onto the nanoporous supportsurface. It is believed that the gold is deposited mainly in elementalform, although other oxidation states may be present. Although gold ismobile and will tend to accumulate in low energy sites of the surface,the nanoporous characteristics of the support and the preferred use ofactivating agents in the practice of the present invention help toimmobilize the gold, helping to keep the deposited gold clustersisolated and preferably discontinuous, This helps to preserve catalyticactivity that might be otherwise compromised if the gold were toaccumulate into larger sized bodies. As an alternative, very thin, goldfilms of nanoscale thickness may also be formed over some or all of thesupport surface if desired, keeping in mind that catalytic activitydecreases with increasing film thickness. Even though such films may beformed with catalytic activity, discontinuous, isolated gold clusterstend to be much more catalytically active and are preferred in mostapplications.

Optionally, the heterogeneous catalyst system may be thermally treatedafter gold deposition if desired. Some conventional methods may requiresuch thermal treatment in order to render the gold catalytically active.However, gold deposited in accordance with the present invention ishighly active as deposited without any need for a thermal treatment.Indeed, such gold can very effectively catalytically oxidize CO to formCO₂ at room temperature or even much cooler. Additionally, dependingupon factors such as the nature of the support, the activating agents,the amount of gold, or the like, catalytic activity can be compromisedto some degree if thermally treated at too high a temperature. Indeed,for some modes of practice in which the heterogeneous catalyst system isintended to be used in a heated environment, e.g., an environment havinga temperature higher than about 200° C., the catalytic activity of thesystem should be confirmed at those temperatures. Embodiments of theinvention that perform catalytically well for CO oxidation in such hightemperature regimes are described below in the examples. These includesystems in which the support includes one or more of alumina, titania,silica, and/or the like.

It is also believed that low-coordination gold in catalyticnanoparticles is beneficial. Low coordination gold refers to Au_(n) forwhich n on average is in the range of 1 to 100, preferably about 2 to20. Without wishing to be bound by theory, we propose that the catalyticactivity of the very small clusters of gold is associated at least tosome degree with low-coordination defects, and that these defects areable to provide sites for storing charges which may be transferred fromunderlying supports and/or other sources. Accordingly, with such defectsand mechanism in mind, it is preferred that heterogeneous catalysts ofthe invention include one or more of the following features: (a) Thegold and hence the defects are located mainly on the surface of theunderlying support; (b) The average value for n is greater than about 2,and (c) As much as is practically possible, gold clusters are isolatedbut nonetheless close to each other (within a distance of about 1-2 nmor less). (d). While such features may be associated with smaller sizedgold clusters, it is possible that such characteristics may be foundmainly at steps or edges of larger clusters.

In addition to gold, one or more other catalysts could also be providedon the same supports and/or on other supports intermixed with thegold-containing supports. Examples include one or more of silver,palladium, platinum, rhodium, ruthenium, osmium, copper, iridium, or thelike. If used, these may be co-deposited onto the support from a targetsource that is the same or different than the gold source target.Alternatively, such catalysts may be provided on the support eitherbefore or after the gold. Other catalysts requiring a thermal treatmentfor activation advantageously may be applied onto the support and heattreated before the gold is deposited. In certain cases catalysts such asRh, Pd and Pt can be deposited according to the present invention andutilized as catalysts without the presence of gold.

In the practice of the present invention, catalytically active gold isdeposited onto one or more nanoporous supports to thereby form aheterogeneous catalyst system. Nanopores can be observed and nanoporesize can be measured via transmission electron microscopy. Thenanoporous nature of a support may also be characterized by a techniquesuch as described in ASTM Standard Practice D 4641-94 in which nitrogendesorption isotherms are used to calculate the pore size distribution ofcatalysts and catalyst supports in the range from about 1.5 to 100 nm.Nanoporous means that the total nanoporous capacity for pores in thesize range of 1 to 10 nm is greater than 20% (i.e., greater than about0.20 using the formula below) of the total pore volume of the supportmaterial in the range from 1 to 100 nm as calculated using the followingformula with data obtained from ASTM D4641-94, the entirety of which isincorporated herein by reference:

${NPC} = \frac{{CPv}_{1} - {CPv}_{10}}{{CPv}_{1} - {CPv}_{100}}$

-   NPC—Nanoporous Capacity-   CPν_(n)—Cumulative Pore Volume at Pore Radius ‘n’ (MM³/G)×10⁻³-   n—Pore Radius (in nanometers)

The nanoporous characteristic of the support helps to immobilize goldclusters on the support surface. This stabilization of the very smallgold particles and clusters is evidenced by both the direct observationof smaller particles of gold in TEM studies of materials possessingnanoporous surfaces and in higher catalytic activity as measured by theability of the catalyst to convert CO to CO₂ in the presence of air.

The nanoporous characteristic of the support helps to immobilize goldclusters on the support surface. This stabilization of the very smallgold particles and clusters is evidenced by both the direct observationof smaller particles of gold in TEM studies of materials possessingnanoporous surfaces and in higher catalytic activity as measured by theability of the catalyst to convert CO to CO₂ in the presence of air.Advantageously, gold is also readily deposited onto nonporous supportsusing PVD in a catalytically active state without requiring additionalthermal or other treatment for activation. In addition to nanoporosity,the substrate particles optionally may further have microporous,mesoporous, and/or macroporous characteristics as such are defined inapplicable provisions of IUPAC Compendium of Chemical Technology, 2dedition (1997). A typical population of activated carbon or aluminasupport particles will tend to include a combination of nanoporous,microporous, mesoporous, and macroporous properties.

It is important to note that the support materials only need benanoporous in the exterior surface region of the support at a depthequal to or greater than the penetration depth of the gold atoms in thepresent invention. Thus, the present invention includes methods wherebynormally low surface area, non-nanoporous materials can be made topossess exterior surfaces characterized by nanoporosity. These methodsinclude adsorption of nanoporous materials such as gels and nanoparticlesize colloids on the surface of a material to form the nanoporousmaterial; hydrolysis of metal alkoxides or metal salts on the surface ofa material to form the nanoporous materials; and oxidation of a thincoating of metal, e.g., aluminum, titanium, tin, antimony or the like,on the surface of a material to form a nanoporous material. In thelatter case, the thin metal films can be deposited by physical vapormethods and the oxidation can be carried out by dry or moist air toproduce a nanoparticle film on the substrate.

In the case of hydrolysis of metal alkoxides, as exemplified herein,hydrolysis with gas phase water is generally more effective in producingactivating nanoporous films than hydrolyzing with liquid phase water orwater solutions.

The support(s) may be used in various shapes or combinations such as,for example, powder, particle, pellet, granule, extrudate, fiber, shell,honeycomb, plate, or the like. The particles can be regular in shape,irregular, dendritic, dendrite-free, or the like. Preferred supports areparticulate in nature or powders.

A particularly preferred support is prepared by adsorbing or adheringfine (less than 100 micrometers, preferably less than 50 micrometers andmost preferably less than 10 micrometer) nanoporous particles on coarser(greater than 30 mesh) particles. Thissmall-particle-supported-on-a-larger-particle composite structureprovides dramatically higher total exterior surface area while retainingthe desirable gas passing characteristics, i.e., low pressure drop, of acoarser particle. In addition, by using nanoporous, smaller particles inconstructing these composite particles, inexpensive, non-nanoporous,coarser particles can be used. Thus, very inexpensive, highly activecatalyst particles can be prepared since the bulk of the volume of acatalyst bed is taken up by the inexpensive, underlying, coarserparticles. Examples of nanoporous small particles that can be used inthis fashion include sol-gel-derived small particles, nanoporous, fineparticle size zeolites, and high surface area aerogel particles.

In constructing the composite support particles, the small particles canbe adhered to the larger particles using partially hydrolyzed alkoxidesolutions, basic metal salt solutions, or nanoparticle sized colloidalmetal oxides and oxy-hydroxides as an adhesion agent. Partiallyhydrolyzed alkoxide solutions are prepared as is well known in thesol-gel art. Useful metal alkoxides include alkoxides of titanium,aluminum, silicon, tin, vanadium and admixtures of these alkoxides.Basic metal salts include nitrate and carboxylate salts of titanium andaluminum. Nanoparticle size colloidal materials include colloids ofoxides and oxy-hydroxides of aluminum, titanium and oxides of silicon,tin, and vanadium. The adhesion agent is present in solution andgenerally is included at an amount of 2 to about 50 oxide weight percentof the nanoporous small particle size material to be adhered.

To construct the composite support particles one of two preferredmethods may be generally used. In one method, the nanoporous, smallparticle size material is admixed with the selected adhesion agent insolution and then this mixture is combined with the coarser particles.If the coarser particle is porous, the small particle-adhesion agentsolution mixture can be introduced by incipient wetting of the porouslarger particle. If the larger particle is not porous, the smallparticle-adhesion agent solution mixture can be admixed with the coarserparticles and the solution liquid can be removed either concurrent withthe mixing or subsequent to the mixing. In either case, after combiningthe nanoporous, small particle size material, the adhesion agent and thecoarser particles and removing the liquid from the solution, the mixtureis dried and calcined to provide a composite particle having thesmaller, nanoporous particles adhered on the surface of a coarserparticle. The calcining temperature is selected to be below thetemperature at which the nanoporous particles lose porosity. Generallythe calcining temperature will be in the range of 200° C. to 800° C.

Particulate embodiments of support media may have any of a wide range ofsizes. Support particle size generally may be expressed in terms of amesh size. A typical expression for mesh size is given by “a×b”, wherein“a” refers to a mesh density through which substantially all of theparticles would fall through, and “b” refers to a mesh density that issufficiently high so as to retain substantially all of the particles.For example, a mesh size of 12×30 means that substantially all of theparticles would fall through a mesh having a mesh density of 12 wiresper inch, and substantially all of the particles would be retained by amesh density having a density of 30 wires per inch. Support particlescharacterized by a mesh size of 12×30 would include a population ofparticles having a diameter in the range from about 0.5 mm to about 1.5mm.

Selecting an appropriate mesh size for the substrate particles involvesbalancing density and catalytic rate against air flow resistance.Generally, a finer mesh size (i.e., smaller particles) tends to providenot only greater catalytic rate and filter capacity, but also higher airflow resistance. Balancing these concerns, “a” is typically in the rangeof 8 to 12 and “b” is typically 20 to about 40 with the proviso that thedifference between a and b is generally in the range from about 8 toabout 30. Specific mesh sizes found to be suitable in the practice ofthe present invention include 12×20, 12×30, and 12×40.

In addition to nanoporosity, support media of the present inventionpreferably further include one or more additional characteristics. Forinstance, preferred embodiments of the support media are characterizedby multiphasic, e.g., biphasic, surfaces. Multiphasic means that thesurface has more than one phase. Our data shows that catalytic activityis enhanced when gold is deposited onto a multiphasic surface. While notwishing to be bound, it is believed that the resultant phase boundarieson the surface appear to help stabilize gold. TEM studies as describedherein and as is well known in the art can be used to assess whether asurface is biphasic. It is believed that these phase boundaries are veryfinely dispersed at the nanoscale, helping to make the boundarieseffective for immobilizing gold.

Multiphasic characteristics may be provided by treatment of a supportwith one or more activating agents. As one example, Ba(NO₃)₂ is one typeof activating agent that may be added to a support prior to golddeposition via solution impregnation followed up with a calciningtreatment. Consider an embodiment in which barium nitrate is used as anactivating agent for a gamma alumina support. When the resultantmaterials are investigated using X-ray diffraction, an isolated bariumphase is not detected. While not wishing to be bound, it is believedthat the barium has reacted onto the alumina support surface, thusmodifying the surface. Consequently, it is believed that the surface hasaluminum rich regions constituting one phase and a barium rich regionconstituting another phase. Each phase has different properties anddifferent affinity to gold. Hence, the phase boundaries, in one belief,function in a manner analogous to fencing to prevent migration andaccumulation of gold. Activating agents are described further below.

A wide variety of materials may serve as suitable supports in thepractice of the present invention. Representative examples includecarbonaceous materials, silicaceous materials (such as silica), metalcompounds such as metal oxides or sulfides, combinations of these, andthe like. Representative metal oxides (or sulfides) include oxides (orsulfides) of one or more of magnesium, aluminum, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium,germanium, strontium, yttrium, zirconium, niobium, molybdenum,technetium, ruthenium, rhodium, palladium, silver, cadmium, indium,iron, tin, antimony, barium, lanthanum, hafnium, thallium, tungsten,rhenium, osmium, iridium, and platinum.

Examples of carbonaceous substances include activated carbon andgraphite. Suitable activated carbon particles may be derived from a widevariety of source(s) including coal, coconut, peat, any activatedcarbon(s) from any source(s), combinations of at least two of these,and/or the like.

Preferred embodiments of support media may be selected from aluminousoxides, titania, titania-alumina, activated carbon, binary oxides suchas hopcalite (CuMnO₂), molecular sieves, and/or the like. Of these,alumina, titania and activated carbon are particularly preferred supportmaterials. Activated carbon, titania and alumina are found in formscharacterized by nanoporosity and therefore, these forms are preferredsupport materials. Activated carbon is advantageous because in additionto providing a support for catalytic activity, the carbon also functionsas an absorbent for noxious gases. Activated alumina also is a preferredsupport material, as it is very robust to aging and heat. Heterogeneouscatalyst systems are advantageously made from ingredients comprising analumina support when the catalyst system will be used at elevatedtemperature and/or where longer service life is desired.

Heterogeneous catalyst systems of the present invention optionally mayincorporate one or more activating agents to enhance catalyticperformance of the system. As used herein, an activating agent generallyrefers to any ingredient that is generally not catalytic by itself yetcan enhance the performance of a catalyst when both the activatingagent(s) and the catalyst are incorporated into the system.

One preferred class of activating agents of the present inventionincludes one or more metal salts. Clearly, the use of such a metal saltenhances catalytic performance, but the exact mechanism by whichperformance is enhanced is not known for certain. Without wishing to bebound, it is believed that the metal cation reacts with the surface ofthe support in a manner that helps to immobilize gold (e.g., byproviding a multiphasic surface) and/or that the metal cation functionsas an electron acceptor or participates in some fashion in the catalyticreaction sequence.

Examples of metal salts include salts of the alkali or alkaline earthmetals such as lithium, sodium, magnesium, calcium, and/or barium. Othermetals include Cs, Ru, and the like. Combinations of any of these metalsalts may be used. In some embodiments, the activating agent comprisesat least one alkali metal salt and at least one alkaline earth metalsalt, wherein the weight ratio of the alkali metal salt to the alkalineearth metal salt is in the range of about 1:19 to about 19:1, preferablyabout 1:3 to about 3:1. For instance, the catalytic performance of asystem comprising a potassium salt and a barium salt on a nanoporousalumina support with gold catalyst is astounding as shown in theexamples below. Briefly, this system catalytically oxidized nearly allCO in a test stream containing 1500 ppm CO at ambient temperature for asustained period of time.

The metal salts can include any suitable counter anion(s). Examplesinclude nitrate, hydroxide, acetate, carbonate, combinations of these,and the like. Carbonate is an especially preferred anion as it appearsindependently to have activating characteristics. Carbonate is even moreeffective when used in combination with an alkali metal or alkalineearth metal. Accordingly, preferred activating agents of the inventioncomprise a carbonate salt, and more preferably an alkali metal carbonatesalt or an alkaline earth metal carbonate salt.

Potassium carbonate is very effective, for example, especially when usedon activated carbon with a gold catalyst, but it is also effective insystems with other types of supports, e.g., alumina, as well. The factthat potassium carbonate activates a carbon-gold system is quitesurprising. Firstly, depositing gold onto K₂CO₃ in the absence of thecarbon or other nanoporous support provides a system with very low, ifany, catalytic activity. Further, depositing gold on activated carbon inthe absence of the K₂CO₃ also provides a system with very low, if any,catalytic activity. Yet, when the three ingredients are combined, a veryeffective catalyst system results as shown by the examples below.Indeed, discovering such a simple and effective way to make activatedcarbon as a support for catalytically active gold is a significantaccomplishment. The benefits of the carbonate is highlighted by datashowing that potassium sulfate is a poor activating agent, although itis believed that its performance would improve if a support impregnatedwith potassium sulfate were to be thermally treated prior to golddeposition.

Yet, potassium carbonate and many of the other salts mentioned hereinare very soluble in aqueous solution. Depositing the gold onto thesubstrate via PVD allows systems containing both gold and suchactivating materials to be easily made. Water soluble activators such asK₂CO₃ cannot be used with conventional aqueous impregnation orprecipitation methods. This is because they would dissolve in and bewashed from the support medium by the water solvents.

Another advantageous class of activating agents includes alkoxidematerials, especially those described above with respect to formingnanoporous surface features on less porous host particles. Preferredalkoxides include alkoxides of Ti and Al. Alkoxide materials areadvantageously used in combination with one or more of the water solublesalt materials described above. When the two kinds of materials are usedtogether, they can be impregnated onto the support at the same time orsequentially in any order, although it is preferred that the alkoxidematerial(s) be impregnated onto the support after the impregnation ofthe salt(s). In a representative process, the water soluble salt isimpregnated onto the support, and the support is then dried andoptionally calcined. Next, the alkoxide is impregnated onto the support,the product is hydrolyzed, dried, and optionally calcined. Thus,prepared, gold is then deposited onto the activated support.

Use of an alkoxide as an impregnant/activating agent appears to changethe crystalline structure of the support in our TEM studies.Specifically, the grain structure of the support proximal to the supportsurface appears to be much finer than the core region and much finerthan otherwise identical systems prepared without the alkoxide. Thestructure modification penetrates in most instances further into thesupport than the gold, e.g., 50 nm or more. In some instances, theboundary between the modified surface region and the unmodified coreregion is easily observed.

Not all alkoxides may work in all conditions. For example, Ti and Alalkoxides were found to enhance catalytic performance when incorporatedinto catalyst systems as shown in the examples. However, substituting aZr-based alkoxide into these formulations did not demonstrate anyenhancement in the ability of the system to oxidize CO.

In a similar fashion, some water soluble salt activating agents,particularly sulfates, oxalates, and phosphates, did not demonstrateactivating performance in some of our studies, although it is believedthat calcining the impregnated support could improve performance of atleast the sulfates and oxalates. While not wishing to be bound, it isbelieved that these kinds of anions, which tend to be coordinating,impact support surface charges in a manner that impairs the ability ofthe surface to immobilize gold. Yet, sulfate and oxalate anions arereadily decomposed at reasonable calcining temperatures, which mayexplain why we believe that calcining would enhance the activatingcharacteristics of these materials.

Iron salts also are poor candidates for use as the only activating agentwhen PVD techniques are used to deposit gold. This is unexpected,inasmuch as iron salts are effective activators when gold is impregnatedonto particles via solution processing. This shows that ingredients thatreadily work in one context, e.g., solution processing, may not work thesame in another context, e.g., PVD processing.

Likewise, not all porous supports are readily activated under the sameconditions that work with other support media. For instance, certainzeolites, e.g., sodium Y zeolites form poor support media when processedin ways that are effective for alumina, carbon, silica, hopcalite, etc.Even when activated with a salt, low or no catalytic activity for COoxidation was observed when procedures that worked for alumina wereapplied to zeolite media. Zeolites are known to have more orderedstructures and to not possess the defects of other oxides. Silicalite,the aluminum-free form of ZSM-5-type zeolite, was found to work well inthe present invention. Thus, for certain zeolite materials to be used assupport media, they are preferably surface treated in some fashion toenhance the ability of the surface to immobilize gold.

The amount of activating agent used in the heterogeneous catalyst systemcan vary over a wide range and will depend upon a variety of factorsincluding the nature of the activating agent, the amount of gold to beincorporated into the system, the nature of the support, and the like.Generally, if too little activating agent is used, the potentialbenefits of using the activating agent may not be fully attained. On theother hand, beyond some point, using additional activating agent may notprovide significant additional benefit and may undermine catalyticperformance to some degree. Accordingly, as suggested guidelines,representative embodiments of the invention may include from 0.25 to 15,preferably 1 to 5 weight percent of activating agent based upon thetotal weight of activating agent and the support. When one or more watersoluble salts and one or more alkoxide materials are used incombination, the molar ratio of the salt(s) to alkoxide(s) ingredient(s)is in the range of 1:100 to 100:1, preferably 1:5 to 5:1.

The activating agent may be incorporated into the heterogeneous catalystsystem in a variety of different ways. In some instances, the support tobe used may inherently include a suitable activating agent. For example,activated carbon derived from coconut shell naturally includes potassiumcarbonate as a constituent. This kind of activated carbon provides anexcellent support for gold catalyst without requiring additionalactivating ingredients.

We have demonstrated the benefit of using activated carbon from coconuthusk as well as the benefit of using potassium carbonate as anactivating agent. Kuraray GC carbon and Kuraray GG carbon are bothderived from coconut shells. Kuraray GG carbon is the natural, resultantcarbon that includes potassium carbonate.

Kuraray GC carbon is similar except that it has been acid washed andthen extensively rinsed with water to remove the potassium carbonate andother acid and water soluble constituents. When gold is deposited ontothese two carbons using PVD, the system derived from Kuraray GG carbon(includes the potassium carbonate) is a very good catalyst for COoxidation, especially under more humid conditions. On the other hand,the system derived from Kuraray GC carbon (essentially no potassiumcarbonate) has low activity for CO oxidation in dry or humidenvironments. Further, if the Kuraray GG carbon is washed to remove thepotassium salt, catalytic functionality of the resultant system issignificantly compromised. Catalytic activity can be recovered again ifthe washed Kuraray GG carbon is impregnated with an activating agentprior to gold deposition, especially if the impregnated carbon isthermally treated (described further below) prior to gold deposition.

TEM (transition electron micrograph) examination of the gold depositedon Kuraray GG carbon particles by physical vapor deposition showed thepresence of nanoparticles and protodots both on the immediate surface ofthe support and in pores immediately adjacent to the support surface. Ascould be seen in the transition electron micrograph, the gold waspresent in both nanoparticle and in very small cluster forms. The goldparticles formed preferentially in small grooves and fissure-like poresin the carbon as evidenced by the orientation of the gold particles inlinear, necklace-like patterns on the surface of the carbon. The darkfield image of the same region showed the gold-enriched striationsclearly. The uniformity of the gold deposition could be clearly seen onthe TEM images. The gold clusters that were observed by TEM were assmall as 1 nm or less and as large as about 5 nm. The gold rich goldgrooves or striations were as wide as about 7 nm and as long as about 50to 100 nm. There were also gold-rich domains comprising exceedingly finegold arrays that appear as veil-like bright regions in the dark fieldimage. It is unknown why these regions, although quite crystalline incharacter, did not coalesce into single crystals of gold.

Although not wishing to be bound by theory, a possible explanation forthe performance of potassium carbonate is that potassium carbonateprovides sites where water can adsorb. Indeed, in certain cases we havefound that the gold catalysts are more active in the presence ofmoisture.

Unlike Kuraray GG carbon, many other desirable supports do not naturallyinclude an activating agent. Consequently, in some instances, it may bedesirable to incorporate an activating agent comprising one or moreconstituents into the desired support. Such incorporation can occur inany desired manner. Incipient wetness impregnation is one suitabletechnique, and examples of using solution impregnation are described inthe examples below. Briefly, incipient wetness impregnation involvesslowly adding a solution comprising the desired activating agent to drysupport particles with mixing. The solution generally is added untilsaturation, and adding an excess of solution is desirably avoided. Suchsolutions typically are aqueous and the concentration of each species ofactivating agent in the solution generally is in the range of from about0.2 M to about 2.5 M. If more than one species of activating agent is tobe added, these may be added together, separately, or in overlappingfashion. After impregnation, the particles are dried and optionallycalcined (thermal treatment).

Deposition of gold preferably occurs via PVD after impregnation, drying,and optional calcining Bifurcation of impregnation and gold depositionis a distinct advantage for many reasons. First, if the gold were to beadded to the particles via solution impregnation, the kinds ofactivating agents that could be used would be limited. For instance,HAuCl₄, a gold species commonly used in solution methods because of itsrelatively low cost, is very acidic making it incompatible with basicactivating agents such as the preferred alkali and alkaline earth metalsalts. In cases where basic gold species are used, the aqueousimpregnation would tend to wash away some of the desired activatingions. Thus, subsequent deposition of gold via PVD (a non-solutionprocess) separate from impregnation with activating agents is asignificant process feature that allows gold to be substantially moreeasily used in combination with these extremely effective activatingagents. As an additional advantage, this method allows gold to bedeposited onto the support with the activating agent already in place.We think this is one reason why gold deposited in accordance with ourinvention is so active as deposited without requiring a subsequentthermal treatment.

Thermal treatment (calcining) of the activated support prior to golddeposition, however, can be very beneficial. In some instances, anactivating agent may not function to the desired degree until aftercalcining. For example, calcining tends to yield demonstrableimprovements when the activating agent includes a nitrate salt. In otherinstances, the performance of an effective activating agent would befurther enhanced. For example, the performance of generally effectivecarbonate salts can be enhanced to a degree via calcining Yet, saltssuch as potassium carbonate tend to already be in active form whenimpregnated, and the resultant activated supports are beneficiallydried, e.g., at a temperature up to about 200° C. without really needinga calcining treatment.

In general, thermal treatment involves heating the impregnated supportat a temperature in the range of 125° C. to about 1000° C. for a timeperiod in the range of 1 second to 40 hours, preferably 1 minute to 6hours, in any suitable atmosphere, such as air; an inert atmosphere suchas nitrogen; carbon dioxide; argon; or a reducing atmosphere such ashydrogen; and the like. The particular thermal conditions to be usedwill depend upon factors including the nature of the support and thenature of the impregnants(s). Generally, thermal treatment should occurbelow a temperature at which the constituents of the impregnated supportwould be decomposed, degraded, or otherwise unduly thermally damaged.Many calcining treatments of impregnated supports are described in theexamples below.

Although an activating agent may be supplied as a salt or the like, theresultant form of the salt or its constituent ions after incorporationinto the heterogeneous catalyst system is not known with certainty.Analysis by x-ray diffraction shows no distinct oxide or carbonate phaseof metal, although some carbonate per se is shown. It is believed,therefore, that the metal ions have reacted with and modified thesupport surface.

There is a wide range of applications for catalysts of the presentinvention. We believe that these catalysts will find application in theareas of treatment of automobile exhaust, as hydrogenation catalysis, ascatalysts for the oxidation of hydrocarbons, and as catalysts for theremoval of the oxides of nitrogen, and in sensors for detection andmeasurement of gases and vapors, and CO removal from inhabited areas.Respiratory protection devices such as smoke masks or escape hoods couldusefully employ catalysts of the invention for the removal of hazardousCO or other gases from breathing air.

The present invention will now be further described in the followingillustrative examples.

Test Method 1: CO Challenge Test Procedure

FIG. 4 shows testing system 50 that was used to subject samples to COchallenges in order to assess catalytic characteristics for oxidizingCO. High-pressure compressed air from supply line 52 is reduced inpressure, regulated, and filtered by regulator 54 (3M Model W-2806 AirFiltration and Regulation Panel, 3M Company, St. Paul, Minn.) to removeparticulates and oils. The regulator is adjusted to give a deliverypressure of between 40 and 60 psi. Valve 56 (Hoke Inc., Spartanburg,S.C.) is used to set the desired main airflow rate as measured by a flowmeter 58 (Gilmont®, Barnant Co, Barrington, Ill.) with a range of 0 to77 LPM. The flow meter 58 was calibrated using a Gilibrator® bubble flowmeter (Sensidyne, Inc., Clearwater, Fla.; not shown). Unless otherwisestated an airflow rate of 64 LPM was used for all catalyst testing.

The main airflow passes through the headspace 60 above a heateddistilled water bath 62 of vessel 64 and then passes via lines 57 and 75into a 1000 ml mixing flask 66. Relative humidity in the mixing flask ismonitored using a RH sensor 68 (Type 850-252, General Eastern,Wilmington, Mass.). The RH sensor 68 provides an electrical signal to ahumidity controller 70 (an Omega Engineering PID controller seriesCN1200 from Omega Engineering Inc., Stamford, Conn.) that delivers powervia lines 71 to a submerged heater 72 to maintain the RH at the setpoint. Unless otherwise indicated, the relative humidity is controlledat 85%.

A cylinder 74 of carbon monoxide equipped with a regulator 76 suitablefor CO service provides a regulated flow of CO gas via line 73. Astainless steel, very fine angled metering valve 78 (Swagelok Co, Solon,Ohio) is used to set the desired CO flow rate. Unless otherwiseindicated, a CO flow rate of 96 mL/min is used in order to obtain a COconcentration in the air stream of 1500 ppm. The metered CO is combinedwith the humidified air in the mixing flask 66.

The combined stream then flows into the test chamber 80 having a box 81such as an inverted, 13-quart, stainless steel bucket closably engaginga support platform 83. Inside the test chamber 80 is a test fixture 82.The test chamber 80 is sealed to support platform 83 using a foam gasket(not shown). Two clamps (not shown) ensure a tight seal to the supportplatform 83. The box 81 can be removed to allow catalyst text fixturesto be placed inside for testing and taken out after testing is complete.The support platform 83 is equipped with an inner 29/42 tapered fitting(not shown) onto which the fixture 82 containing the catalyst to betested is mounted.

The CO and CO₂ concentrations and the dew point temperature are measuredat the outlet of the test chamber using a Brüel & Kjær Multi-gas MonitorType 1302 sensor (Brüel & Kjær, Nærum, Denmark; not shown) equipped withoptical filters #982 to detect CO₂ and #984 to detect CO. The Multi-gasMonitor was calibrated with 10,000-ppm CO₂ and 3,000-ppm CO gasstandards following the manufacturers recommended procedure. TheMulti-gas Monitor outputs data to a data acquisition device such as achart recorder or a laptop PC running Hyperterminal Software (Hilgraeve,Monroe, Mich.). Text files are imported into Microsoft® Excel software(Microsoft Corp., Redmond, Wash.) for data analysis. Prior to initiatingtesting the system 50 is allowed to equilibrate to a constantconcentration of nominally 1500-ppm CO. Variability in the initial COconcentration was ±5% for samples tested at 1500-ppm and ±3% for samplestested at 3600-ppm CO. The temperature of the air stream is monitoreddownstream of the test fixture using a K-type thermocouple (not shown)and digital readout (not shown) (Fluke 51 K/J Thermometer, FlukeCorporation, Everett, Wash.).

Catalyst samples are sieved to remove fines prior to testing. Unlessotherwise specified, samples were sieved to remove particles finer than20 mesh using U.S. Standard Sieves (A.S.T.M. E-11 specification; TheMurdock Co., Mundelein, Ill.). A specified catalyst volume, typically100 ml, is loaded into the aluminum test fixture 82 with 8.9 cm (3.5 in)inner diameter and equipped with an outer 29/42 tapered fitting using aloading column (as described in UK 606,876 with one modification, theremoval of the upward-facing cone). Typical bed depth is approximately1.6 cm (0.6 in). Screens mounted inside the test fixture 82 prevent lossof catalyst particles during the testing. When the measured COconcentration has stabilized, the tubing 85 carrying the air/CO mixtureis disconnected from the top of the test chamber 80 via the taperedfitting (not shown), the box 81 is removed, and the test fixture 82containing the catalyst is placed on the 29/42 fitting on the supportplatform 81. The box 81 is replaced and sealed to the support platform83. CO and CO₂ concentration measurements begin when the air/CO tubing85 is reconnected to the tapered fitting on the top of the test chamber80. Measurements continue for a specified time period, typically 30minutes.

For tests run at 64 LPM with 3600-ppm CO, valve 78 was replaced with astainless steel, fine metering, double pattern valve (Swagelok Co.,Solon, Ohio) to allow for control of higher CO flowrates.

Test Method 2: Chromatographic Test Procedure and Apparatus

FIG. 5 shows a system 100 used for chromatographic analysis of catalyticcharacteristics of samples. System 100 includes a high pressure CO inair mixture (1.9% v/v) stored in tank 102 and is also coupled to asource 104 of building compressed air via line 106. Pressure regulatorand shut off valve 101 and fine needle valve 103 help control the flowof CO in air through line 105. The flow of CO in air is measured byrotameter 107 (Alphagaz (Air Liquide) 3502 flow tube, Morrisville, Pa.).

The flow of building compressed air through line 106 is reduced inpressure, regulated, and filtered by regulator 110 (3M Model W-2806 AirFiltration and Regulation Panel, 3M Company, St. Paul, Minn.). Theregulator is adjusted to give a delivery pressure of between 40 and 60psi. Fine needle valve 112 is used to set the desired airflow ratethrough line 106.

The flows of CO in air and the building compressed air are combined atjuncture 108 to provide a CO in air mixture of the desired concentrationand flow rate. Rotameter 114 (Aalborg Instruments 112-02 flowtube,Orangeburg, N.Y.) on line 116 measures the total flow of the combinedstreams. The rotameters are calibrated using a Gilibrator® bubble flowmeter (not shown) placed at the catalyst bed (no catalyst present). Thetwo rotameters 107 and 114 are chosen to obtain concentrations fromabout 1000 to 20,000 ppm CO at flow rates from about 100 mL/min to about500 mL/min under lab ambient conditions.

The diluted CO in air mixture in line 116 is then humidified to thedesired RH by passing the air mixture either through the inner tube of atube in shell Nafion® dryer 118 as shown (Perma Pure MD 110-12P; TomsRiver, N.J.) operating as a humidifier or by passing the air mixturethrough a pressure vessel containing water (not shown). Wet air isintroduced to dryer 118 through line 120 and exits via line 122. In thelatter, process, a RH of about 70% was obtained at a flow rate of 200ml/min. Wet air is passed through the dryer shell to humidify the dry COin air stream passing through the inner tube. The wet air is obtained bybubbling compressed air through a glass frit into a flask of watermaintained at a controlled temperature in a refrigerated water bath. Ifa lower RH is desired, the temperature of the water bath is lowereduntil the CO in air mixture attains the desired RH. This is measured bya General Eastern Hygro-M1 optical mirror dew point hygrometer (GEGeneral Eastern Instruments, Wilmington Mass.). Room temperature airsaturated with water vapor at about 3 L/min through the dryer shellhumidifies a CO/air stream at 100 mL/min to >90% RH

The catalyst sample (usually about 1-2 cm in depth) is snowflaked into asection of thick walled 4 mm ID polyethylene tubing 124 about 8 cm inlength to form a catalyst bed 125. A cotton plug 127 seals one end oftubing 124. The CO in air mixture passes through the catalyst bed andthen through a particulate cartridge filter 126 (Balston DFU samplefilter grade BQ, Parker Hannifin Corporation, Tewksbury, Mass.) into thegas sampling valve of a gas chromatograph 128 (SRI model 8610C gaschromatograph with gas sampling valve and thermal conductivity andhelium ionization detectors, Torrance, Calif.). The particulate filter126 protects the GC valve from damage by particulates escaping thecatalyst bed.

The gas sampling valve periodically injects the exit stream from thecatalyst bed onto a 5 ft molecular sieve 5A column. This separates COfrom air. CO concentration is determined by either a thermalconductivity detector (CO detection limit about 500 ppm) or by a heliumionization detector (CO detection limit <10 ppm). The CO concentrationis measured approximately every four minutes during the test, displayed,and recorded in a data file.

These detectors are calibrated by diluting a known flow of Scottcertified CO (99.3%) with a known flow of air to generate known COconcentrations (flow calibrator: Sensidyne Gilibrator flow calibrator,Clearwater, Fla.). A calibration curve is generated from these data.

Gold Application Method: Process for Deposition of Gold Nanoparticlesonto Substrate Particles:

The apparatus described in the detailed description and shown in FIGS. 2and 3 is used as follows to prepare catalytic materials according to thefollowing procedure, unless expressly noted otherwise. 300 cc ofsubstrate particles are first heated to about 200° C. in air overnight(120° C. in the case of carbon substrates) to remove residual water.They are then placed into the particle agitator apparatus 10 while hot,and the chamber 14 is then evacuated. Once the chamber pressure is inthe 10⁻⁵ torr range, the argon sputtering gas is admitted to the chamber14 at a pressure of about 10 millitorr. The gold deposition process isthen started by applying a cathodic power of 0.03 kilowatts. Theparticle agitator shaft 40 is rotated at about 4 rpm during the golddeposition process. The power is stopped after 60 minutes. The chamber14 is backfilled with air and the gold coated particles are removed fromthe apparatus 10. The gold sputter target 32 is weighed before and aftercoating to determine the amount of gold deposited. In the case of carbonparticles, the amount of gold deposited was determined by ion-coupledplasma elemental analysis on the treated carbon particles to be 0.05%w/w.

During the deposition process the gap between the blades 42 and thechamber wall were maintained at 1.7 mm (deposition condition 1) or 2.7mm (deposition condition 2).

Preparation of Gamma Alumina Particles:

Room temperature deionized water (2600 ml), 48 g of 16 N analyticalgrade nitric acid and 800 g alpha alumina monohydrate (boehmite) powdersold under the trade designation DISPERAL were charged into an 18.9liter polyethylene-lined steel vessel. The charge was dispersed at highspeed for five minutes using a Gifford-Wood Homogenizer Mixer (GreecoCorp., Hydson, N.H.). The resulting sol was poured into a 46 cm×66 cm×5cm polyester-lined aluminum tray where it was dried in a air oven at100° C. to a friable solid.

The resulting dried material was crushed using a “Braun” type UDpulverizer having a 1.1 mm gap between the steel plates. The crushedmaterial was screened and the 0.125 mm to about 1 mm screen sizematerial was retained and was fed into the end of a calciner which was a23 cm diameter 4.3 meter long stainless steel tube having a 2.9 meterhot zone, the tube being inclined at 2.4 degrees with respect to thehorizontal, and rotating at 7 rpm, to provide residence time of about15-20 minutes. The calciner had a hot zone feed end temperature of about350° C. and exit end temperature of about 800° C. The gas above thealumina particles at the hot end of the calciner was measured at about380° C. during the calcinations. The pre-fired material was thenscreened to be greater than 20 mesh but less than 16 mesh in size usingU.S. Standard Sieves (A.S.T.M. E-11 specification; The Murdock Co.,Mundelein, Ill.). This size fraction was designated alumina particles“A”. An additional sample of the pre-fired material was screened to begreater than about 20 mesh but less than 14 mesh in size using the U.S.Standard Sieves (A.S.T.M. E-11 specification; The Murdock Co.,Mundelein, Ill.). The 14 to 20 mesh particle size samples weredesignated alumina particles “B”. These materials were used in thepreparation of the following catalyst supports.

Example 1 Type A Gamma Alumina Particles

Type A gamma alumina particles were treated with gold by plasma-assistedsputtering as previously described using deposition condition 2. Theperformance of the CO oxidation catalyst of example 1 in oxidizing COduring gas flow through a bed was measured using test method 1. The COchallenge was 3600 ppm CO and the total gas flow rate was 64 liters/min.The gas was at 85% relative humidity. The results are represented inFIG. 6. FIG. 6 and other similar graphs in these examples displaymeasured gas concentrations in ppm versus time of testing after test gasmixture is passed through a 100 ml test bed. The elapsed time isrepresented in minutes:seconds:tenths of seconds.

Example 2 Un-Modified Type B Gamma Alumina Particles

Type B gamma alumina particles were treated with gold by plasma-assistedsputtering as previously described using deposition condition 2. Theperformance of the CO oxidation catalyst of example 2 in oxidizing COduring gas flow through a bed was measured using test method 1. The COchallenge was 3600 ppm CO and the total gas flow rate was 64 liters/min.The gas was at 85% relative humidity. The results are represented inFIG. 7.

Impregnation of Gamma Alumina Particles:

A solution of the impregnation liquid was prepared by mixing sufficientsoluble salt of the impregnation metal with deionized water insufficient quantity to generate a solution having the desiredconcentration. As an example, to prepare a 0.5 M solution of potassiumcarbonate (FW=138.21 g/mole), 69.11 g of potassium carbonate wasdissolved in sufficient deionized water to yield a final volume of 1liter.

The particles were impregnated by incipient wetness. The incipientwetness technique involves slow addition of the impregnation solution tothe dry, gamma alumina particles while stirring the particles with apaddle or spatula, until the pores of the gamma alumina particles arefully saturated with the solution via impregnation of the solution intothe pores of the gamma alumina particles. An excess of the impregnationsolution, as evidenced by the visual observation of liquid phase on orbetween the particles was avoided. After the particles were fullysaturated, the impregnated particles were dried in a forced air oven at130° C. and were calcined as described for each sample.

Example 3 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Sample Heated to 130° C.

710 g of gamma alumina particles A (950 ml volume of gamma aluminaparticles) was impregnated by the incipient wetness technique using a0.5 M K₂CO₃ (Merck KgaA, Darmstadt, Germany) solution. After an additionof 469 ml of the 0.5 M K₂CO₃ full saturation was achieved. This resultsin a catalyst support, after drying that is about 2.5% by weightpotassium. The particles were dried at 130° C. and a 300 ml portion ofthis sample was treated with gold (deposition condition 2).

The weight percent gold on this sample was measured by InductivelyCoupled Argon Plasma Spectroscopic Analysis (ICP). The results forreplicate samples were 0.0486 wt % gold and 0.0521 wt % gold.

A sample from Example 3 was examined by TEM as previously described. Theapproximate size range of Au particles in an undulating region thatappeared to be representative of the sample was 2.1 to 6.6 nm. Theaverage size of Au particles in this region was 3.0 nm and theapproximate range of depth into the substrate was 38 to 60 nm. In a flatregion of the sample, the approximate size range of Au particles was 2.4to 11.4 nm. The average size of Au particles in this region was 8.6 nmand the gold particles were found to be entirely on the surface of theparticle with little penetration observed.

The performance of the catalyst of example 3 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 8. These results illustrate the improvedcatalytic properties of the support modified with a potassium source.

Example 4 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Sample Heated to 300° C.

A 300 ml portion of the dried sample from example 3 was calcined to 300°C. by heating in air in a box furnace and holding the sample at 300° C.for 1 hour. After cooling, this calcined sample was treated with gold(deposition condition 2).

The performance of the catalyst of example 4 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 9.

Example 5 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Sample Heated to 600° C.

A 300 ml portion of the dried sample from example 3 was calcined to 600°C. by heating in air in a box furnace and holding the sample at 600° C.for 1 hour. After cooling, this calcined sample was treated with gold(deposition condition 2).

The performance of the catalyst of example 5 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 10.

Example 6 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Effect of Potassium Carbonate Content

A solution of potassium carbonate was prepared by dissolving 6.91 g ofK₂CO₃ ((Merck KGAA, Darmstadt, Germany)) in sufficient deionized waterto yield a volume of 200 ml. A sample of gamma alumina particles B (300ml volume of particles, 224.14 g) was impregnated by the incipientwetness technique using about 150 ml of the 0.4 M K₂SO₄. Afterimpregnation, the particles were dried in an oven at 130° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 6 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 11.

Example 7 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Effect of Potassium Carbonate Content

Potassium carbonate impregnated gamma alumina particles were preparedand tested exactly as described in example 6 with the exception that13.82 g of potassium carbonate was used in place of the 6.91 g potassiumcarbonate. The results of testing are represented in FIG. 12.

Example 8 Preparation of Potassium Carbonate Impregnated Gamma AluminaParticles—Effect of Potassium Carbonate Content

Potassium carbonate impregnated gamma alumina particles were preparedand tested exactly as described in example 6 with the exception that20.72 g of potassium carbonate was used in place of the 6.91 g potassiumcarbonate. The results of testing are represented in FIG. 13.

Example 9 Preparation of Ammonium Carbonate Impregnated Gamma AluminaParticles

A solution of 0.5 M ammonium carbonate (Fisher Scientific Co., FairLawn, N.J.) was prepared by dissolving 11.41 g of ammonium carbonatehydrate in sufficient deionized water to yield a volume of 200 ml. Asample of gamma alumina particles A (300 ml volume of particles, 224.14g sample) was impregnated by the incipient wetness technique using about150 ml of the 0.5 M ammonium carbonate solution. After impregnation, theparticles were dried in an oven at 100° C. After drying the impregnatedparticles were gold treated via plasma-assisted sputtering (depositioncondition 2).

The performance of the catalyst of example 9 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 14.

Example 10 Preparation of Potassium Hydroxide Impregnated Gamma AluminaParticles

A solution of 0.4 M potassium hydroxide was prepared by dissolving 4.49g of KOH (Merck KgaA, Darmstadt, Germany) in sufficient deionized waterto yield a volume of 200 ml. A sample of gamma alumina particles A (300ml volume of particles, 224.14 g sample) was impregnated by theincipient wetness technique using about 150 ml of the 0.4 M KOH. Afterimpregnation, the particles were dried in an oven at 100° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 10 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 15.

Example 11 Preparation of Potassium Acetate Impregnated Gamma AluminaParticles

A solution of 0.4 M potassium acetate was prepared by dissolving 7.85 gof KCH₃O₂ (Fisher Scientific Co., Fair Lawn, N.J.) in sufficientdeionized water to yield a volume of 200 ml. A sample of gamma aluminaparticles A (300 ml volume of particles, 224.14 g) was impregnated bythe incipient wetness technique using about 150 ml of the 0.4 M KCH₃O₂.After impregnation, the particles were dried in an oven at 100° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 11 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 16.

Example 12 Preparation of Potassium Sulfate Impregnated Gamma AluminaParticles

A solution of potassium sulfate was prepared by dissolving 13.94 g ofK₂SO₄ (J.T. Baker Chemical Co., Phillipsburg, N.J.) in sufficientdeionized water to yield a volume of 200 ml. A sample of gamma aluminaparticles A (300 ml volume of particles, 224.14 g) was impregnated bythe incipient wetness technique using about 150 ml of the 0.4 M K₂SO₄.After impregnation, the particles were dried in an oven at 100° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 12 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 17.

Example 13 Preparation of Potassium Oxalate Impregnated Gamma AluminaParticles

A solution of potassium oxalate was prepared by dissolving 14.74 g ofK₂C₂O₄ (Mallinkrodt Chemical Works, St. Louis, Mo.) in sufficientdeionized water to yield a volume of 200 ml. A sample of gamma aluminaparticles A (300 ml volume of particles, 224.14 g) was impregnated bythe incipient wetness technique using about 150 ml of the 0.4 M K₂C₂O₄.After impregnation, the particles were dried in an oven at 100° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 13 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 18.

Example 14 Preparation of Potassium Phosphate Impregnated Gamma AluminaParticles

A solution of potassium phosphate was prepared by dissolving 13.93 g ofK₂HPO₄ (Aldrich Chemical Co., Milwaukee, Wis.) in sufficient deionizedwater to yield a volume of 200 ml. A sample of gamma alumina particles A(300 ml volume of particles, 224.14 g) was impregnated by the incipientwetness technique using about 150 ml of the 0.4 M K₂HPO₄. Afterimpregnation, the particles were dried in an oven at 100° C. Afterdrying the impregnated particles were gold treated via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 14 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 19.

Example 15 Preparation of Barium Impregnated Gamma AluminaParticles—Dried at 130° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M barium nitrate (Certified A.C.S., FisherScientific Co., Fair Lawn, N.J.) solution as the impregnation solution.This impregnation involved impregnating 224.1 g of the gamma aluminawith 148 ml of a solution prepared by dissolving 20.9 g of bariumnitrate in deionized water to yield a final volume of 200 mls. Afterdrying at 130° C. the sample was treated with gold via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 15 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 20.

Example 16 Preparation of Barium Impregnated Gamma AluminaParticles—Calcined to 300° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M barium nitrate (Certified A.C.S., FisherScientific Co., Fair Lawn, N.J.) solution as the impregnation solutionexactly as described in example 12. After drying at 130° C., a portionof the sample was calcined to 300° C. and held at 300° C. for 1 hourbefore allowing to cool with the furnace. After cooling, the sample wastreated with gold via plasma-assisted sputtering (deposition condition2).

The performance of the catalyst of example 16 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 21.

Example 17 Preparation of Barium Impregnated Gamma AluminaParticles—Calcined to 600° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M barium nitrate (Certified A.C.S., FisherScientific Co., Fair Lawn, N.J.) solution as the impregnation solutionexactly as described in example 12. After drying at 130° C., a portionof the sample was calcined to 600° C. and held at 600° C. for one hour.After cooling, the sample was treated with gold via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 17 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 22.

Comparison of the results of example 17 with those of example 16 andexample 15 demonstrate that the activating effect of barium nitrate isstrongly manifested after the impregnated support was heated to 600° C.

Example 18 Preparation of Potassium Carbonate Treated—Barium ImpregnatedGamma Alumina Particles—Calcined to 600° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M barium nitrate (Certified A.C.S., FisherScientific Co., Fair Lawn, N.J.) solution as the impregnation solutionexactly as described in example 12. After drying at 130° C., a portionof the sample was calcined to 600° C. and held at 600° C. for one hour.After cooling, this sample was impregnated with 0.5 M K₂CO₃ by incipientwetness. The sample was dried at 130° C. and treated with gold accordingto deposition condition 2.

The performance of the catalyst of example 18 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 23.

Comparison of the results of testing the material of example 18 with theresults of testing the material of example 17 show that improvement incatalytic performance can be attained by using a combination ofactivating agents.

Example 19 Preparation of Magnesium Impregnated Gamma AluminaParticles—Dried at 130° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M magnesium nitrate hexahydrate (Alfa Aesar,Ward Hill, Mass.) solution. The solution for impregnation was preparedby dissolving 20.51 g of the magnesium nitrate hexahydrate in deionizedwater to yield a final volume of 200 ml. 148 ml of this solution wasused to impregnate 224.14 g of the alumina particles. After drying at130° C. the sample was treated with gold via plasma-assisted sputtering(deposition condition 2).

The performance of the catalyst of example 19 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 24.

Example 20 Preparation of Magnesium Impregnated Gamma AluminaParticles—Calcined to 300° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M magnesium nitrate (Alfa Aesar, Ward Hill,Mass.) solution as described in example 16. After drying at 130° C., aportion of the sample was calcined to 300° C. and held at 300° C. for 1hour before allowing to cool with the furnace. After cooling, the samplewas treated with gold via plasma-assisted sputtering (depositioncondition 2).

The performance of the catalyst of example 20 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 25.

Example 21 Preparation of Magnesium Impregnated Gamma AluminaParticles—Calcined to 600° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 0.4 M magnesium nitrate (Alfa Aesar, Ward Hill,Mass.) solution as described in example 16. After drying at 130° C., aportion of the sample was calcined to 600° C. and held at 600° C. forone hour. After cooling, the sample was treated with gold viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 21 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 26.

Comparison of the results of example 21 with those of example 20 andexample 19 demonstrate that the activating effect of magnesium nitrateis strongly manifested after the impregnated support was heated to 600°C.

Example 22 Preparation of Calcium Impregnated Gamma AluminaParticles—Dried at 130° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M calcium nitrate. To preparethe impregnation solution, 18.89 g of calcium nitrate tetrahydrate(BAKER ANALYZED®, J. T. Baker, Co., Phillipsburg, N.J.) was dissolved indeionized water to yield a volume of 200 ml. 148 ml of this solution wasimpregnated into 224.14 g of the gamma alumina particles. After dryingat 130° C. the sample was treated with gold via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 22 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 27.

Example 23 Preparation of Calcium Impregnated Gamma AluminaParticles—Calcined to 300° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M calcium nitrate (calciumnitrate tetrahydrate, BAKER ANALYZED®, J. T. Baker, Co., Phillipsburg,N.J.) as described in example 19. After drying at 130° C., a portion ofthe sample was calcined to 300° C. and held at 300° C. for 1 hour beforeallowing to cool with the furnace. After cooling, the sample was treatedwith gold via plasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 23 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 28.

Example 24 Preparation of Calcium Impregnated Gamma AluminaParticles—Calcined to 600° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M calcium nitrate (calciumnitrate tetrahydrate, BAKER ANALYZED®, J. T. Baker, Co., Phillipsburg,N.J.) as described in example 19. After drying at 130° C., a portion ofthe sample was calcined to 600° C. and held at 600° C. for one hour.After cooling, the sample was treated with gold via plasma-assistedsputtering (deposition condition 2).

The performance of the catalyst of example 24 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 29.

Comparison of the results of example 24 with those of example 23 andexample 22 demonstrate that the activating effect of calcium nitrate ismanifested after the impregnated support was heated to 600° C.

Example 25 Preparation of Potassium Carbonate-Treated, CalciumImpregnated Gamma Alumina Particles—Calcined to 600° C.

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M calcium nitrate (calciumnitrate tetrahydrate, BAKER ANALYZED®, J. T. Baker, Co., Phillipsburg,N.J.) as described in example 19. After drying at 130° C., a portion ofthe sample was calcined to 600° C. and held at 600° C. for one hour.After cooling, the sample was impregnated by incipient wetness using a0.5 M solution of potassium carbonate. The resulting calcium andpotassium treated particles were dried at 135° C. overnight and treatedwith gold via plasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 25 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 30.

Example 26 Preparation of Iron Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M iron nitrate nonahydrate. Tomake the iron nitrate solution, 32.32 g of Fe(NO₃)₃.9H₂O (CertifiedA.C.S., Fisher Scientific Co., Fair Lawn, N.J.) was dissolved indeionized water to yield a final volume of 200 ml. 224.14 g of gammaalumina A particles were impregnated with the iron nitrate solution.After drying at 130° C., the sample was calcined to 600° C. and held at600° C. for 1 hour. After calcining the impregnated particles were goldtreated via plasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 26 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 31.

Example 27 Preparation of Manganese Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with 148 ml of a solution of 50% manganese nitrate(Fisher Scientific Co., Fair Lawn, N.J.). 224.14 g of gamma alumina Aparticles were impregnated with the manganese nitrate solution. Afterdrying at 130° C., the sample was calcined to 600° C. and held at 600°C. for 1 hour. After calcining the impregnated particles were goldtreated via plasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 27 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 32.

Example 28 Preparation of Cobalt Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M cobalt nitrate hexahydrate.To make the cobalt nitrate solution, 23.28 g of Co(NO₃)₂.6H₂O(analytical reagent grade, Mallinkrodt Inc., Paris, Ky.) was dissolvedin deionized water to yield a final volume of 200 ml. 224.14 g of gammaalumina A particles were impregnated with the cobalt nitrate solution.After drying the impregnated particles at 130° C., a portion of thesample was calcined to 600° C. and held at 600° C. for 1 hour. Aftercalcining the impregnated particles were gold treated viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 28 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 33.

Example 29 Preparation of Copper Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M copper (II) nitrate 2.5hydrate. To make the copper nitrate solution, 18.61 g of Cu(NO₃)₂.2.5H₂O(BAKER ANALYZED®, J. T. Baker, Co., Phillipsburg, N.J.) was dissolved indeionized water to yield a final volume of 200 ml. 224.14 g of gammaalumina A particles were impregnated with the copper nitrate solution.After drying the impregnated particles at 130° C., a portion of thesample was calcined to 600° C. and held at 600° C. for 1 hour. Aftercalcining the impregnated particles were gold treated viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 29 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 34.

Example 30 Preparation of Nickel Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M nickel nitrate hexahydrate.To make the nickel nitrate solution, 23.26 g of Ni(NO₃)₂.6H₂O (Cobaltlow, certified, Fisher Scientific Company, Fair Lawn, N.J.) wasdissolved in deionized water to yield a final volume of 200 ml. 224.14 gof gamma alumina A particles were impregnated with the nickel nitratesolution. After drying the impregnated particles at 130° C., a portionof the sample was calcined to 600° C. and held at 600° C. for 1 hour.After calcining the impregnated particles were gold treated viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 30 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 35.

Example 31 Preparation of Chromium Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M chromium nitrate nonahydrate.To make the chromium nitrate solution, 32.01 g of Cr(NO₃)₃.9H₂O (Reagentgrade, Matheson, Coleman and Bell, Norwood, Ohio) was dissolved indeionized water to yield a final volume of 200 ml. 224.14 g of gammaalumina A particles were impregnated with the chromium nitrate solution.After drying the impregnated particles at 130° C., a portion of thesample was calcined to 600° C. and held at 600° C. for 1 hour. Aftercalcining the impregnated particles were gold treated viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 31 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 36.

Example 32 Preparation of Zinc Impregnated Gamma Alumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of 0.4 M zinc nitrate hexahydrate. Tomake the zinc nitrate solution, 23.80 g of Zn(NO₃)₂.6H₂O (BAKER ANALYZEDReagent®, Mallinkrodt Baker, Inc., Phillipsburg, N.J.) was dissolved indeionized water to yield a final volume of 200 ml. 224.14 g of gammaalumina A particles were impregnated with the zinc nitrate solution.After drying the impregnated particles at 130° C., a portion of thesample was calcined to 600° C. and held at 600° C. for 1 hour. Aftercalcining the impregnated particles were gold treated viaplasma-assisted sputtering (deposition condition 2).

The performance of the catalyst of example 32 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 37.

Example 33 Preparation of Titanium and Potassium Impregnated GammaAlumina Particles

The incipient wetness technique was used to impregnate A-type gammaalumina particles with a solution of Tyzor LA™ titanium lactate solutioncontaining potassium carbonate. To make the titanium lactate/potassiumcarbonate solution, 6.91 g of K₂CO₃ was dissolved in 200 ml of Tyzor LAtitanium lactate (E. I. Du Pont de Nemours Co., Willmington, Del.: TyzorLA is nominally 13.7% by weight TiO₂ equivalent). 224.14 g of gammaalumina A particles were impregnated with about 148 ml of the TyzorLA/potassium carbonate solution. After drying the impregnated particlesat 130° C., a portion of the sample was calcined to 600° C. and held at600° C. for 1 hour. After calcining the impregnated particles were goldtreated via plasma-assisted sputtering (deposition condition 2).

The sample was examined by TEM as previously described. The approximatesize range of Au particles in a representative region of the sample was3.2 to 32 nm. The average size of Au particles was 9 nm and theapproximate range of depth into the substrate was 33 to 60 nm. Theperformance of the catalyst of example 33 was examined for its catalyticactivity in oxidizing CO during gas flow through a bed using testmethod 1. The CO challenge was 3600 ppm CO and the total gas flow ratewas 64 liters/min. The gas was at 85% relative humidity. The results arerepresented in FIG. 38.

Metal Oxide-Coated Substrates Example 34 Preparation of TitaniumOxide-Coated Alumina Particles

A solution of tetraisopropyltitanate (TPT) in isopropyl alcohol wasprepared by mixing 30 ml of tetraisopropyltitanate (Gelest, Inc.,Tullytown, Pa.) with sufficient isopropyl alcohol to yield a finalvolume of 148 ml. This solution was impregnated by incipient wetnessinto 224.14 g of the B-type alumina particles. After impregnation theparticles were spread out onto a 30×21 cm aluminum tray and were allowedto hydrolyze in air for about 2 hours. During this time the particleswere gently stirred every 10 minutes using a spatula. The tray of airhydrolyzed-TPT-treated particles was transferred into an oven and driedat about 150° C. overnight. After drying, the titanium oxide-coatedparticles were calcined at 500° C. (time at temperature=1 hour, heatingrate from room temperature to 500° C.=1.6° C./min.). After cooling theseparticles were gold treated via sputtering (deposition condition 2).

The performance of the catalyst of example 34 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 39.

Example 35 Preparation of Titanium Oxide-Coated Alumina Particles withLiquid Water Hydrolysis

Titania-coated alumina particles were prepared as described in example31 with the exception that rather than allowing thetetraisopropyltitanate to hydrolyze in air prior to drying, after thetreatment with the TPT-isopropyl alcohol mixture, the particles werewashed twice with 500 ml of deionized water. The particles were thendried at 150° C. overnight. After drying, the titanium oxide-coatedparticles were calcined at 500° C. (time at temperature=1 hour, heatingrate from room temperature to 500° C.=1.6° C./min.). After cooling theseparticles were gold treated via sputtering (deposition condition 2).

The performance of the catalyst of example 35 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 40.

Example 36 Preparation of Titanium Oxide-Coated, PotassiumCarbonate-Treated Alumina Particles

Potassium carbonate-treated alumina particles were prepared byimpregnating A-type alumina particles with a solution of 0.5 M K₂CO₃(Merck KGaA, Darmstadt, Germany) in deionized water. This material wasdried overnight at 135° C. in a forced air furnace. A solution oftetraisopropyltitanate (TPT) in isopropyl alcohol was prepared by mixing30 ml of tetraisopropyltitanate (Gelest, Inc., Tullytown, Pa.) withsufficient isopropyl alcohol to yield a final volume of 148 ml. Thissolution was impregnated by incipient wetness into 224.14 g of thepotassium carbonate-treated, A-type alumina particles. Afterimpregnation the particles were spread out onto a 30×21 cm aluminum trayand were allowed to hydrolyze in air for about 2 hours. During this timethe particles were gently stirred every 10 minutes using a spatula. Thetray of air hydrolyzed-TPT-treated particles was transferred into anoven and dried at about 150° C. overnight. After drying, the titaniumoxide-coated particles were calcined at 500° C. (time at temperature=1hour, heating rate from room temperature to 500° C.=1.6° C./min.). Aftercooling these particles were gold treated via sputtering (depositioncondition 2).

The performance of the catalyst of example 36 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 41.

The results of the testing of the material of example 36 demonstratesthe high activity that can be obtained by use of a nanoporous metaloxide coating in combination with an activating agent.

Example 37 Preparation of Zirconium Oxide-Coated Gamma Alumina Particles

30.0 g of zirconium n-propoxide (Johnson Matthey Electronics, Ward Hill,Mass.) was diluted with isopropyl alcohol to a final combined volume of148 ml. 224.14 g of B-type gamma alumina particles were impregnated byincipient wetness using this solution. The resulting material was airhydrolyzed for about 5 hours, and dried in an oven at 135° C. overnight.After drying, the titanium oxide-coated particles were calcined at 500°C. (time at temperature=1 hour, heating rate from room temperature to500° C.=1.6° C./min.). After cooling these particles were gold treatedvia sputtering (deposition condition 2).

The performance of the catalyst of example 37 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 42.

Particles of example 37 were placed in a ½ mm high, 3 mm diameter copperring on a microscope slide and immobilized using conductive Buehlerepoxy. The conductive epoxy was prepared by mixing 5 g Buehler epoxybase (Epoxy Base No. 20-8130-037, Buehler Inc., Lake Bluff, Ill.), 1 gBuehler Epoxy hardener (No 20-8132-003) and 1 g colloidal carbon glue(Catalog number 16053, Ted Pella, Inc., Redding, Calif.). The epoxy mixwas de-aired at 5 mm vacuum for 2 minutes, poured into the ring and overthe particles. The samples were cured for 1 hr. at 70° C. and the copperring holding the samples immobilized in epoxy was removed from themicroscope slide. The immobilized sample was polished flat on one sidewith 600 grit carbide sand paper. The flat surface was affixed to aSouthBay 515 dimpling machine (South Bay Technology, Inc., San Clemente,Calif.) and ground using diamond slurry to a thickness of 15 um.

The Sample was placed in a Gatan ion mill (Gatan Duo Mill Model 600,Gatan, Inc., Warrendale, Pa.) and milled with dual guns using argon at5KV and 0.5 mA per gun until the sample was perforated in the correctarea. The sample/s were viewed in a JEOL JSL 200CX (JEOL USA Inc.,Peabody, Mass.) at 200 Kv. The samples were manipulated so as to allowviewing of the outer surface of the gold particle with a viewing angleperpendicular to the catalyst surface.

The microstructure and the condition of the core-coating interfaced wasdetermined and the crystalline phases of the core-interface determined.The core was transition alumina, the coating zirconia, and the Au didnot visibly penetrate the core. The zirconia phase was discontinuous andthe gold was primarily found on the outside edge of the zirconiadeposit. Selected area diffraction was used to identify the majorcrystalline phases present. Crystalline gold, gamma alumina andcrystalline zirconia were identified. The zirconia phase was identifiedas monoclinic zirconia. The zirconia crystallites were in 0.1-0.3micrometer clusters consisting of primary crystallites of 50-100 nm.Although some small gold crystallites were observed in the 30-100 nmsize range, the bulk of the gold was found to be much larger, in the30-100 nm range.

This example shows that the zirconia did not function to stabilize thegold in the nanoparticle and nanocluster form. This larger particle sizegold was found to be essentially inactive as a CO oxidation catalyst.

Example 38 Preparation of Aluminum Oxide-Coated Gamma Alumina Particles

30.0 g of aluminum sec-butoxide (Johnson Matthey Electronics, Ward Hill,Mass.) was diluted with sec-butanol to a final combined volume of 148ml. 224.14 g of B-type gamma alumina particles were impregnated byincipient wetness using this solution. The resulting material was airhydrolyzed for about 5 hours, and dried in an oven at 135° C. overnight.After drying, the aluminum oxide-coated particles were gold treated viasputtering (deposition condition 2).

The sample was examined by TEM as previously described. The approximatesize range of Au particles in a representative region of the sample was2.6 to 9.7 nm. The average length of Au particles in this region was 4.4nm and the approximate range of depth into the substrate was 40 to 57nm.

The performance of the catalyst of example 38 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 43.

The results of the testing of the material of example 38 show the highperformance of a catalyst utilizing a support material whose surface wasaltered by the hydrolysis of a metal alkoxide (in this case an aluminumalkoxide) on said surface (in this case a nanoporous aluminum oxide).

Example 39 Gold Treated Glass Beads

280 grams of solid glass spheres, 170×325 mesh, obtained from PottersIndustries Inc. (Valley Forge, Pa.) were gold treated using depositioncondition 1. The cathodic power was 0.03 kW, the agitator speed wasapproximately 4 rpm, the argon pressure was approximately 4 mT, and thetreatment time was 2 hours. The sample was tested as described in TestMethod 2 using 5400 ppm CO in air at greater than 70% RH and a flow rateof 200 ml/min. The bed depth was approximately 1 inch. The results areindicated in FIG. 44.

Example 40 Preparation of Titanium Oxide-Coated, PotassiumCarbonate-Treated Alumina Particles—Effect of Sequence of Addition

A solution of tetraisopropyltitanate (TPT) in isopropyl alcohol wasprepared by mixing 30 ml of tetraisopropyltitanate (Gelest, Inc.,Tullytown, Pa.) with sufficient isopropyl alcohol to yield a finalvolume of 148 ml. This solution was impregnated by incipient wetnessinto 224.14 g of the B-type alumina particles. After impregnation theparticles were spread out onto a 30×21 cm aluminum tray and were allowedto hydrolyze in air for about 2 hours. During this time the particleswere gently stirred every 20 minutes using a spatula. The tray of airhydrolyzed-TPT-treated particles was transferred into an oven and driedat about 150° C. overnight. After drying, the titanium oxide-coatedparticles were calcined at 500° C. (time at temperature=1 hour, heatingrate from room temperature to 500° C.=1.6° C./min.). After cooling theseparticles were impregnated by incipient wetness technique with a 0.5 MPotassium carbonate (Merck KGaA, Darmstadt, Germany) solution. Thismaterial was dried overnight at 135° C. in a forced air oven. Afterdrying, the potassium carbonate impregnated-titanium oxide-coatedparticles were gold treated via sputtering (deposition condition 2).

The performance of the catalyst of example 40 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 45.

Example 41 Gold Treatment on Acid-Washed Carbon Granules

1000 ml 12×20 mesh size Kuraray GC (Kuraray Chemical Company, Ltd.,Osaka, Japan) was washed with a solution of 2000 ml of deionized watercontaining 4 ml of concentrated NH₄OH (EM Industries, Incorporated,Gibbstown, N.J.) followed by washing with deionized water to neutral pH.The washed sample was dried at 120° C. for 24 hours. This material wasgold treated via sputtering (deposition condition 1).

The performance of the catalyst of example 41 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 46.

Example 42 Gold Treatment on a Treated Carbon Granule: Effect ofImpregnation of a Potassium Source

123.80 g 12×20 mesh size Kuraray GC (Kuraray Chemical Company, Ltd.,Osaka, Japan) was impregnated by incipient wetness with a solution ofpotassium acetate. The potassium acetate solution was prepared bydissolving 7.50 g potassium acetate (Fisher Scientific, Fair Lawn, N.J.)in 142.50 g deionized water). After impregnation, the sample was driedin an oven at 130° C. overnight and subsequently calcined in a flow ofnitrogen gas according to the heating schedule: room temperature to 950°C. at 3° C./min. and then hold at 950° C. for 1 hour. After cooling thismaterial was gold treated via sputtering (deposition condition 1).

The performance of the catalyst of example 42 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 32 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 47.

Example 43 Gold Treatment on a Treated Carbon Granule: Effect ofImpregnation of a Sodium Source

123.80 g 12×20 mesh size Kuraray GC (Kuraray Chemical Company, Ltd.,Osaka Japan) was impregnated by incipient wetness with a solution ofsodium acetate. The sodium acetate solution was prepared by dissolving7.50 g sodium acetate (Mallinkrodt Incorporated, St. Louis, Mo.) in142.50 g deionized water. After impregnation, the sample was dried in anoven at 130° C. overnight and subsequently calcined in a flow ofnitrogen gas according to the heating schedule: room temperature to 950°C. at 3° C./min. and then hold at 950° C. for 1 hour. After cooling thismaterial was gold treated via sputtering (deposition condition 1). Theperformance of the catalyst of example 43 was examined for its catalyticactivity in oxidizing CO during gas flow through a bed using testmethod 1. The CO challenge was 1500 ppm CO and the total gas flow ratewas 32 liters/min. The gas was at 85% relative humidity. The results arerepresented in FIG. 48.

Example 44 Gold Treatment on Non-Acid Washed Carbon Granule

12×20 mesh size Kuraray GG was gold treated via sputtering (depositioncondition 1).

The performance of the catalyst of example 44 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 32 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 49.

Example 45 Gold Treatment on Carbon Granule: Effect of Changes inDeposition Conditions

12×20 mesh size Kuraray GG was gold treated via sputtering (depositioncondition 1) with the exception that the particle agitator was turned at10 rpms during the deposition process. The performance of the catalystof example 45 was examined for its catalytic activity in oxidizing COduring gas flow through a bed using test method 1. The CO challenge was1500 ppm CO and the total gas flow rate was 32 liters/min. The gas wasat 85% relative humidity. The results are represented in FIG. 50.

Example 46 Preparation of Surface Area Enhanced Particles: FineParticles Bonded to Coarser Particles

A 10% boehmite sol was prepared by dispersing 20.0 g of alpha aluminamonohydrate (boehmite) powder sold under the trade designation Disperal(Condea Chimie, GMBH) in 188.5 g deionized water using 1.25 mlconcentrated nitric acid as a dispersant. To disperse the boehmite, theboehmite was first added to the deionized water while rapidly stirringwith an OMNI GLH lab mixer (Omni International, Warrenton, Va.). Theacid was added dropwise to the dispersion while rapidly mixing togenerate uniform dispersion. To 135.11 g of this sol was added 15.01 gof fine (40-200 mesh) particles of gamma alumina (gamma alumina preparedby calcining boehmite particles as described earlier). This mixture wasblended well to disperse the gamma alumina particles in the boehmitesol. This boehmite-gamma alumina particle mixture was then added to230.8 g of the type A gamma alumina particles while stirring the type Agamma alumina particles with a spatula so as to effect a uniformtreatment of the type A gamma alumina particles with the boehmite-gammaalumina particle mixture. The result of this process was that the finergamma alumina particles adhered to the surface of the coarser gammaalumina particles. The mixture was transferred to a shallow aluminumtray and dried in an oven at 125° C. The dried particles were calcinedto 600° C. according to the schedule: room temperature to 600° C. at4.8° C./min., hold at 600° C. for 1 hour, and then cool with thefurnace. After the particles were cool, the particles were gold treatedaccording to deposition condition 2.

The performance of the catalyst of example 46 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 32 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 51.

Example 47 Preparation of Surface Area Enhanced Particles: Effect ofSurface Modification through Creation of Surface Roughness and SurfacePorosity

A boehmite sol was prepared by the method described in example 46 using358.52 g of Disperal™ boehmite, 592 g of deionized water and 13 ml ofconcentrated nitric acid. In a separate step, fine particle size gammaalumina was prepared by calcining a sample of Disperal™ boehmite to 600°C. in a fused silica tray (heating rate of 4.8° C./min., held at 600° C.for 2 hours). 58.61 g of this fine particle size gamma alumina was addedto the boehmite sol with rapid stirring using an OMNI GLH lab mixer. 200g of this mixture was diluted with 900 g of deionized water. To thisdispersion was added 50.0 g of the fine (40-200 mesh) gamma aluminaparticles along with 30.0 g of carbon (Darco Activated Carbon, ICIUnited States, Inc., Willmington, Del.) and the mixture was mixed well.150 ml of this mixture was added in fine drops to 224.1 g of Type Bgamma alumina particles while mixing the particles with a spatula. Theresulting particles were uniformly black (black from the carbonparticles in the dispersion). The treated particles were transferred toa shallow aluminum tray and dried in the oven overnight at 120° C. Thedried particles were calcined to 600° C. according to the schedule: roomtemperature to 600° C. at 2.4° C./min., hold at 600° C. for 1 hour, coolwith the furnace. After the particles were cool, the particles wereimpregnated with 0.5 M solution of potassium carbonate by incipientwetness. The particles were again dried at 120 C overnight, calcined to600° C. (4.8° C./min. to 600° C., hold at 600° C. for 1 hour, cool withthe furnace) and, after cooling, the particles were gold treatedaccording to deposition condition 2.

The performance of the catalyst of example 47 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 3600 ppm CO and the total gas flowrate was 64 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 52.

Example 48 Activation of Molecular Sieves through Gold Treatment

300 ml of 14-30 mesh Sigma molecular sieve particles (M2760, 4 angstrommolecular sieves; Sigma Aldrich, St. Louis, Mo.) were treated with goldusing deposition condition 2.

The performance of the catalyst of example 48 was examined for itscatalytic activity in oxidizing CO during gas flow through a bed usingtest method 1. The CO challenge was 1500 ppm CO and the total gas flowrate was 32 liters/min. The gas was at 85% relative humidity. Theresults are represented in FIG. 53.

Examples 49-54 Effect of Changes in Deposition Conditions on theActivity of Carbon Catalysts

Examples 49-54 were prepared by gold treating 300 ml samples of 12×20mesh Kuraray GG carbon particles using the deposition conditions shownin table 1 below. In this table the “power” represents the cathodicpower during the gold deposition process; “current” represents themeasured current during this process; “time” represents the time of goldtreatment; “pressure” represents the chamber pressure during thedeposition process; “revs total” is the number of total revolutions ofthe agitator in the chamber during the deposition time; “gap” indicatesthe gap between the blades and the chamber wall, “<20 mesh” indicatesthe percentage by weight of the sample that was found to pass through a20 mesh sieve after the gold treatment; “<60 mesh” indicates thepercentage by weight of the sample that was found to pass through a 60mesh sieve after the gold treatment; and the “% eff.” is a measure ofthe catalytic activity as measured by the percentage of CO removedduring the first 15 minutes of the test versus the amount of CO that wasintroduced into the catalyst test bed during the test.

TABLE 1 <20 <60 Sample power current time speed pressure revs gap meshmesh % eff. Example (kW) (Amps) (hr) (rpm) (mTorr) total (mm) (%) (%)(%) 49 0.03 0.06 1 4 10 240 1.7 21.4 1.0 97 50 0.03 0.06 1 4 10 240 1.721.1 1.3 98 51 0.03 0.06 1 10 10 600 1.7 22.6 1.8 95 52 0.03 0.06 1 10 3600 1.7 28.0 2.4 97 53 0.06 0.12 0.5 4 10 120 1.7 10.3 0.7 90 54 0.030.06 1 4 10 240 2.7 5.1 0.5 75

The weight percent gold as measured by ICP for these samples isindicated in the following table. Replicate samples of Examples 49 and53 were measured by this technique.

TABLE 2 Example wt % gold 49 0.0657 0.0659 51 0.0939 — 52 0.0995 — 530.0962 0.0923 54 0.0933 —

The performance of the catalyst materials of examples 49-54 wereexamined for their catalytic activities in oxidizing CO during gas flowthrough a bed using test method 1. The CO challenge was 1500 ppm CO andthe total gas flow rate was 32 liters/min. The gas was at 85% relativehumidity. The results are represented in FIG. 54.

Examples 55-60 Effect of Changes in Power on the Gold on Carbon CatalystActivity

Examples 55-60 were prepared by gold treating 300 ml samples of 12×20mesh Kuraray GG carbon particles using the deposition conditions shownin table 2 below. In these examples, “thickness” represents the relativethickness of the gold coating as measured by the plasma current,“rotation rate” represents the rotation speed of the particle agitatorshaft, “distance” represents the length between the sample and thetarget and the other variables are as previously defined.

TABLE 3 rotation thickness power current time rate gap distance % eff.Example (centiAmps) (kW) (Amps) (hrs) (rpm) (mm) (cm) (%) 55 15 0.090.15 1.00 2 2.7 8.6 80 56 12 0.06 0.12 1.00 2 2.7 8.6 72 57 3 0.01 0.031.00 2 2.7 8.6 59 58 9 0.04 0.09 1.00 2 2.7 8.6 77 59 std 0.03 0.06 1.004 2.7 4.6 82 60 6 0.02 0.06 1.00 2 2.7 8.6 65

The performance of the catalyst materials of examples 55-60 wereexamined for their catalytic activities in oxidizing CO during gas flowthrough a bed using test method 1. The CO challenge was 1500-ppm CO andthe total gas flow rate was 32 liters/min. The gas was at 85% relativehumidity. The results are represented in FIG. 55.

Examples 61-65 Effect of Impregnation and Heat Treatment on CatalystPerformance

Samples prepared as described in Examples 1, 3, 4, 5, and 17 anddesignated Examples 61, 62, 63, 64, 65, respectively, were screened toretain particles greater than 40 mesh and smaller than 30 mesh usingU.S. Standard Sieves (A.S.T.M. E-11 specification; The Murdock Co.,Mundelein, Ill.). The retained samples were tested as described in TestMethod 2 using 16,000 ppm CO in air at greater than 85% RH and a flowrate of 100 mL/min. Catalyst mass tested was 435 mg for Examples 61, 62,and 65 and 438 mg for Examples 63 and 64. Results are indicated in FIG.56.

Examples 66-70 Effect of Silica Support and Gold Coating Thickness

Examples 66-70 were prepared by gold treating various chromatographygrade silica gel substrates (S2509, 54883, 59258 obtained from SigmaAldrich Co, St. Louis, Mo.) as described in Table 3 below. 52509consists of 70 to 230 mesh particles (63 to 200 μm) with average porediameter of 60 Å. S4883 consists of 20 to 200 mesh particles (74 to 840μm) with average pore diameter of 22 Å. S9258 consists of 15 to 40 μmparticles with average pore diameter of 60 Å. The distance between thesamples and target was maintained at 4.6 cm. The gap was set at 1.7 mm.The “catalyst weight” refers to the weight of the material tested forits catalytic activity. “Drying temp” refers to the temperature at whichthe sample was dried overnight prior to gold treating.

TABLE 4 Catalyst Drying Rotation Weight Temp Power Current Time rateExample Substrate mg ° C. kW Amps hrs rpm 66 S2509 98 200 0.03 0.07 2 467 S4883 105 200 0.02 0.06 1 4 68 S9258 98 600 0.02 0.1 6 4 69 S9258 105— — — — — 70 S2509 214 200 0.03 0.07 2 4

The performance of the catalytic materials of Examples 66 to 70 wastested as described in Test Method 2. The CO concentration was 1800-ppmCO in air, the relative humidity was >90%, and the gas flow rate was 100mL/min. Results are indicated in FIG. 57.

Example 71 Effect of Long-Time CO Exposure on Catalyst Performance

A sample prepared as described in Example 38 was sieved to retainparticles smaller than 140-mesh using U.S. Standard Sieves (A.S.T.M.E-11 specification; The Murdock Co., Mundelein, Ill.). The retainedsample was tested as described in Test Method 2 using 18,900 ppm CO inair at greater than 85% RH and a flow rate of 100 mL/min. Catalyst masstested was 119 mg. The test was continued for 28 hours. Results areindicated in FIG. 58.

Other embodiments of this invention will be apparent to those skilled inthe art upon consideration of this specification or from practice of theinvention disclosed herein. Various omissions, modifications, andchanges to the principles and embodiments described herein may be madeby one skilled in the art without departing from the true scope andspirit of the invention which is indicated by the following claims.

1. A method of oxidizing CO, comprising the steps of: providing ananoporous support medium, wherein the nanoporous support mediumcomprises physically vapor deposited elemental gold clusters ofdimensions of about 0.5 nm to about 50 nm on the nanoporous supportmedium; and, causing the nanoporous support medium to catalyticallycontact the CO.
 2. The method of claim 1 wherein the oxidizing of COoccurs in a respiratory protection system.
 3. The method of claim 2wherein the oxidizing of CO occurs in a personal respiratory protectionsystem.
 4. The method of claim 3, wherein the personal respiratoryprotection system is selected from the group consisting of a mask and anescape hood.
 5. The method of claim 1, wherein the nanoporous supportmedium comprises at least one water soluble metal salt.
 6. The method ofclaim 5, wherein the at least one water soluble metal salt is selectedfrom the group consisting of an alkali metal, an alkaline earth metal,and mixtures thereof.
 7. The method of claim 1, wherein the nanoporoussupport medium comprises a carbonaceous material.
 8. The method of claim1, wherein the nanoporous support medium comprises activated carbon. 9.The method of claim 1, wherein the nanoporous support medium comprisesalumina.
 10. The method of claim 1, wherein the nanoporous supportmedium comprises titania.
 11. The method of claim 1, wherein thenanoporous support medium comprises a plurality of composite particles,each composite particle comprising a plurality of nanoporous guestparticles incorporated onto a host particle wherein the ratio of theaverage particle size of the host particles to the guest particles is inthe range of 10,000:1 to 10:1.
 12. The method of claim 6, wherein the atleast one water soluble metal salt comprises a potassium salt.
 13. Themethod of claim 12, wherein the at least one water soluble metal saltcomprises potassium carbonate.
 14. The method of claim 8, wherein theactivated carbon comprises potassium carbonate.
 15. The method of claim14, wherein the activated carbon is derived from coconut shells thatnaturally contain potassium carbonate.
 16. The method of claim 15,wherein the nanoporous support media further comprises titania.